PDF Editor
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A browser-based PDF editor that supports text boxes, highlights, underlines, shapes, arrows, freehand pen, bucket fill, and eraser. Powered by pdf-lib and PDF.js, all processing happens locally — your files never leave the device — making it ideal for contract markup, PDF note-taking, and study material annotation.
Related
What is PDF editing?
In the broad sense, PDF editing refers to adding, modifying, or removing content (text, images, comments, shapes) in an existing PDF document. In the narrow sense, it emphasises “modifying original text / replacing words / deleting paragraphs”, which corresponds to the “Edit PDF” mode in Adobe Acrobat.
**The essential difference between the two types:** ① Overlay editing (annotation) — adds a new layer on top of the PDF (text box, highlight, shape, pen, comment) without touching the original content stream, and all marks become standard PDF annotation objects; ② Rewriting editing (redaction / content stream rewrite) — modifies or deletes the original text by rebuilding the content stream, with possible minor font-metric adjustments. This tool focuses on overlay editing, covering about 80% of daily needs.
**Why prefer overlay editing?** ① 100% preserves the original content without breaking the layout; ② every mark is a standard PDF annotation, displayed correctly by any reader (Adobe Reader, browsers, PDF.js, Foxit); ③ text, fonts, and vector elements are never rewritten, so there is zero loss in quality.
**Most common scenarios:** highlighting / underlining key passages while reading a PDF; adding clauses or dates to electronic contracts; marking up textbooks; drawing arrows or boxes on business PDFs; sketching signature drafts. About 90% of annotation needs in study, design, and legal work can be satisfied with overlay editing.
Use Cases
- Add highlights or underlines to key paragraphs while reading a PDF, so you can review and locate them later
- Academic PDF notes: draw lines, write annotations, and mark key points with arrows as you read
- Add dates, supplementary clauses, or revision marks to electronic contracts while overlay annotations keep the original layout intact
- Draw arrows or rectangle frames on a scanned PDF to point at specific errors or instructions
- Add custom notes on top of study materials, user manuals, and API documentation
- Mark up design drafts or reports during review, circling issues and adding red-text feedback
How to Use
- Upload the PDF you want to annotate (drag-and-drop or click to select)
- Pick a tool from the left toolbar: Text, Highlight, Shape, Pen, Eraser, and so on
- Click or drag on the PDF canvas to add content; use the bottom style bar to adjust colour, font size, stroke width, and opacity
- Use the Undo / Redo buttons or Ctrl+Z / Ctrl+Shift+Z to roll back changes; jump pages quickly via the right-side thumbnail panel
- When satisfied, click the “Export PDF” button in the top-right corner to download the annotated PDF file
Features
- Text annotations: eight font sizes from 12 to 48 px, eight preset colours plus a custom colour picker, draggable to reposition after creation
- Highlight / Underline / StrikeOut: standard PDF Markup annotations with adjustable 10–80% opacity, compatible with all PDF readers
- Rectangle / Circle / Arrow: vector shape annotations with optional stroke and fill colours (transparent or custom)
- Bucket fill: pick a fill colour, then click any rectangle or circle to fill it; overlay annotations never modify the original content
- Freehand pen: freely draw a continuous path with the mouse or trackpad, choose 1 / 2 / 4 / 6 px stroke width, exported as a vector curve
- Eraser: paint a white stroke that covers the PDF; when the stroke hits a text annotation, that annotation is removed automatically
- Undo / Redo: Ctrl+Z to undo, Ctrl+Shift+Z to redo, every step can be rolled back
- Zoom 25%–400%: Ctrl + scroll wheel for fast zoom, button step ±20%, one-click reset to 100%
- Multi-page navigation: bottom page jump bar, left/right arrows, and the right-side thumbnail panel for quick positioning
- Pure client-side processing: PDF.js for parsing and pdf-lib for export, files are never uploaded to any server
Best Practices
Undo / redo a few extra times before saving
This tool records the history of every add / delete / move operation, and undo (Ctrl+Z) and redo (Ctrl+Shift+Z) work across tool switches. After finishing a batch of annotations, press Ctrl+Z a few times to check the result, continue once you are happy, and undo a few more steps before exporting to make sure no residue is left behind.
Semantic difference between highlight and underline
Highlight is an overlay (a semi-transparent colour block), ideal for marking “read again / important”. Underline is a line under the text, ideal for emphasising terms or proper nouns. StrikeOut is suitable for “obsolete / rejected”. The same passage can carry several Markup annotations at once, making it easy to grasp at a glance.
Text box vs original editing: pick the right tool
This tool only supports “adding text boxes”; it cannot modify the original text. To fix a typo, the recommended workflow is: convert the PDF to Word with [PDF to Word](/pdf/to-word/), edit in Word, then export back to PDF with [Word to PDF](/pdf/to-word/). Do not try to fake it with the eraser plus a new text box — the white overpaint will show through.
Pick the right scenario for the two eraser effects
Dragging the eraser paints a white stroke that overwrites the original PDF pixels (good for quickly hiding sensitive info); when the stroke hits a user-added text annotation, that annotation is deleted (based on AABB intersection detection). For deleting user annotations, the Select + Delete combo is more precise; for white overpaint, the eraser covers large areas faster.
Coordinating bucket fill and shapes
Draw a rectangle or circle first (drag while in the shape tool) → choose a fill colour on the bottom style bar (transparent / 7 presets / custom picker) → switch to the bucket tool → click inside the rectangle or circle to fill it. The bucket only affects user-drawn shapes, not the original PDF artwork.
Use thumbnails to locate pages quickly
After the PDF loads, the right-side thumbnail panel auto-expands with a 0.3× preview of every page. Click a thumbnail to jump straight to it. For multi-page documents (over 10 pages), thumbnails are faster than the page ← / → buttons.
Zoom and coordinate stability
Ctrl + scroll wheel for fast zoom, and click the percentage button at the bottom-left to reset to 100%. All annotation coordinates are stored in effectiveScale, so positions do not drift after zooming. The export position, however, is based on the effectiveScale at creation time, so add precise annotations near 100% and zoom in to inspect when needed.
Use the PDF compress tool to shrink size after editing
Overlay annotations grow the PDF (about 0.5–2 KB per annotation). A large number of annotations (over 200) or image-bearing annotations can bloat the file noticeably. After exporting, run the file through the [PDF compress tool](/pdf/compress/) for a second pass — perfect for email attachments and mobile sharing.
Combine with other PDF tools
This tool focuses on overlay annotation; combine it for complex structural edits: [extract pages](/pdf/extract-pages/) + [remove pages](/pdf/remove-pages/) + [reorder pages](/pdf/reorder-pages/) for batch changes, [PDF encrypt](/pdf/encrypt/) for secure distribution, [PDF watermark](/pdf/watermark/) for content identification, and [PDF page numbers](/pdf/page-num/) for page-number management. Each tool plays its part, and combining them is more efficient.
FAQ
Can this PDF editor modify the original text?
This tool is an “overlay” editor (annotation) and does not support modifying or deleting the original PDF text. You can add new text boxes, highlights, shapes, pen strokes, and other annotations on top of the PDF, while the original text remains 100% intact. If you need to change the original text, we recommend converting the PDF to Word first, editing in Word, and then converting it back to PDF.
Which annotation tools are supported?
Twelve tools in total: Select (move / delete), Text (12–48 px), Highlight (opacity 10–80%), Underline, StrikeOut, Rectangle, Circle, Arrow, Bucket fill (fill rectangle / circle), Freehand pen, Eraser, and Delete (hover to remove). Every annotation is a standard PDF annotation, so they display correctly in any reader after export.
Is the PDF uploaded to a server?
No. All PDF parsing (PDF.js) and export (pdf-lib) runs locally in your browser; the file never leaves your machine and is cleared when you refresh or close the page. This makes it suitable for sensitive scenarios such as contracts, classified material, and internal documents.
How do I save the edited PDF?
Click the “Export PDF” button in the top-right of the toolbar to download the annotated PDF; the file name starts with “annotated_”. The exported PDF is compatible with Adobe Reader, the built-in PDF viewers in Chrome / Edge / Safari, Foxit, WPS, and all other mainstream readers.
What are the undo / redo shortcuts?
Undo: Ctrl+Z (Cmd+Z on macOS); Redo: Ctrl+Shift+Z (Cmd+Shift+Z on macOS). You can also click the ↶ / ↷ buttons on the bottom toolbar. This tool records the history of every add / delete / modify action, and the history survives tool switches.
What are the two effects of the eraser?
Dragging the eraser paints a white stroke that covers the original PDF text or graphics (overwritten with white pixels); when the stroke touches a user-added text annotation, that annotation is automatically removed (based on AABB intersection detection). For large-area coverage use the eraser; for precise text-box removal use Select + Delete.
What is the difference between Highlight, Underline, and StrikeOut?
Highlight covers the text range with a semi-transparent colour block (yellow by default, opacity 10–80%) and is good for marking important passages. Underline draws a line beneath the text (stroke width 1 / 2 / 4 / 6 px), good for emphasising terms. StrikeOut draws a line through the middle of the text, good for marking “obsolete / rejected” items. All three are standard PDF Markup annotations.
Can I navigate quickly in a multi-page PDF?
Yes. The bottom page-jump bar (← / current page / total / →) lets you switch pages one by one; the right-side thumbnail panel (which auto-expands after the PDF loads) shows a 0.3× preview of every page, and clicking a thumbnail jumps directly to that page. Thumbnails are independent of the edit state and are not regenerated while editing.
What is the difference between Rectangle, Circle, and Arrow?
Rectangle draws a hollow or filled rectangle with optional fill colour, often used to frame regions. Circle draws a hollow or filled ellipse (hold Shift while dragging a square to constrain to a perfect circle), great for emphasising key points. Arrow draws a straight line with an arrowhead from start to end, ideal for pointing at things. All three let you change the stroke and fill colour.
Can I change the font size and colour of a text box?
Yes. After selecting the text tool, the bottom style bar shows a Size dropdown (12 / 14 / 16 / 18 / 20 / 24 / 32 / 48 px) and a colour palette (8 presets + a custom picker). Click the text after adding it to select it, and you can also move it. This tool supports only one font family (Arial / Helvetica) and cannot switch to a Chinese font.
How do I delete an annotation I have added?
Three methods: ① Pick the Delete icon on the annotation toolbar, hover over an annotation to see a red dashed box, and click to remove it; ② switch to the Select tool, click the annotation, then press Delete; ③ press Ctrl+Z to undo the most recent add. For batch deletion, method ② with multi-select is recommended (multi-select is not yet available, so single deletion is fastest with method ①).
Is mobile supported?
Yes. On mobile, the toolbar automatically switches from the left vertical layout on PC to a bottom horizontal layout. Touch gestures are translated to mouse events via touchstart / touchmove / touchend, so all tools (pen, shapes, text, etc.) work on phones and tablets. For the best precision, we recommend using a larger tablet (10 inches or more).
Will the exported PDF grow in size?
Yes, it will. Overlay annotations write a new content stream and add PDF annotation objects. A few annotations (under 20) usually add less than 100 KB; many annotations (over 200) or image-bearing annotations can add more. If you need to shrink the file, run it through the [PDF compress tool](/pdf/compress/) after exporting.
Can I annotate scanned or photocopied PDFs?
Yes. Scans are essentially image-based PDFs, and the highlight, shape, pen, text box, and eraser tools all overlay normally. The eraser’s “white overpaint” is especially handy on scans: paint over the wrong text with a white block, then add new text in the same place.
Glossary
- PDF Annotation
- An “overlay layer” object defined in the PDF standard: text boxes, highlights, underlines, shapes, and pen strokes all exist as separate annotations without modifying the original content stream. Adobe Reader and browser PDF viewers display them correctly.
- Overlay vs rewriting editing
- Overlay editing only adds an annotation layer, leaving the original text untouched; rewriting editing must rebuild the PDF content stream in order to modify or delete original text. This tool is overlay — you can add but not alter, while guaranteeing the original file stays 100% intact.
- Markup annotation
- A sub-type of PDF annotation dedicated to marking text: Highlight, Underline, StrikeOut, Squiggly, and so on. This tool outputs them through the standard pdf-lib annotation API, so compatibility is 100%.
- Bucket fill
- After picking a fill colour, clicking the inside of a rectangle or circle fills that shape with the colour. The fill only affects user-drawn rectangle or circle annotations in this tool and never touches the original PDF content.
- Eraser
- This tool has two effects: ① dragging on the canvas paints a white stroke that covers the original PDF pixels; ② when the stroke touches a user-added text annotation, that annotation is automatically removed (based on AABB intersection detection).
- Freehand pen
- Freely drag the mouse or trackpad to draw a continuous path, with all sampled points recorded smoothly. On export, the points are joined as a vector curve, so the result can be scaled arbitrarily without loss.
- Undo / Redo
- This tool keeps an operation history stack: every completed annotation is pushed onto the history, and the entire sequence is retained. Use Ctrl+Z to undo and Ctrl+Shift+Z to redo, and the history survives tool switches.
- Page thumbnail
- The right-side panel shows a low-resolution preview of every page (a 0.3× shrunken image), and clicking it jumps straight to that page. Thumbnails are independent of the edit state and are not regenerated while editing.
- Zoom and canvas coordinate system
- This tool uses a two-level zoom of fit-to-container auto-fit plus user zoom (25%–400%). Annotation coordinates are stored in effectiveScale, and on export they are converted back to PDF points at that scale to prevent drift after zooming.
PDF annotation tools cheat sheet
Different annotation tools have different visual effects and typical scenarios.
| Tool | Type | Visual effect | Typical scenario |
|---|---|---|---|
| Text | Text annotation | Adds a positionable text box on the page | Add notes, dates, or names |
| Highlight | Markup annotation | Semi-transparent colour block (10–80% opacity) | Mark key points, study notes |
| Underline | Markup annotation | Line beneath the text | Emphasise terms and proper nouns |
| StrikeOut | Markup annotation | Line through the middle of the text | Mark obsolete / rejected clauses |
| Rectangle | Shape annotation | Hollow or filled rectangle (fillable) | Frame areas, hide information |
| Circle | Shape annotation | Hollow or filled ellipse (fillable) | Circle key points, emphasise one item |
| Arrow | Line annotation | Straight line with an arrowhead | Pointing instructions, flow charts |
| Pen | Ink annotation | Freehand curve (vector) | Handwritten signatures, sketches |
| Bucket | Edit tool | Fills an existing rectangle / circle | Emphasis blocks, flow charts |
| Eraser | Edit tool | White overpaint / remove text annotations | Fix errors, clear content |
Overlay vs rewriting PDF editing
This tool is overlay editing; understanding the difference helps you pick the right tool.
| Dimension | Overlay (this tool) | Rewriting (Acrobat etc.) |
|---|---|---|
| Operation type | Add annotations / shapes / text / highlights / pen | Modify or delete original text, insert images |
| Original content | 100% preserved | Rewritten or deleted |
| Font compatibility | No effect | Possible minor layout shifts from font differences |
| Implementation difficulty | Low (annotation API) | High (rewrite the content stream) |
| PDF size | Slightly larger (0.5–2 KB per annotation) | Depends on the operation |
| Reader compatibility | 100% compatible with all readers | Some older readers may misbehave |
| Supported by this tool | ✅ | ❌ |
| Typical scenario | Annotation, notes, emphasis, signatures | Fix typos, redact sensitive info, insert images |
This tool vs Adobe Acrobat vs Foxit vs Sejda
Different tools emphasise different features, prices, privacy, and convenience.
| Dimension | This tool (GeekFormat) | Adobe Acrobat | Foxit PDF Editor | Sejda |
|---|---|---|---|---|
| Deployment | Browser-based | Desktop client | Desktop client | Web online |
| Price | Completely free | Subscription $19.99/month | One-time $129 | Limited free tier |
| File processing location | Local browser | Local | Local | Uploaded to server |
| Text replacement | Not supported | Fully supported | Fully supported | Fully supported |
| Overlay annotation | ✅ 12 tools | ✅ | ✅ | ✅ |
| Privacy | 100% local | Local | Local | Server processing |
| File size limit | Limited by memory (about 200 MB) | None | None | 200 pages / 3 hours |
| Best for | Daily annotation, sensitive files, zero install | Legal / publishing, requires editing original | Enterprise batch processing | One-off small tasks |