Compress PDF
Compress PDF files directly in your browser without uploading them to a server. Pick Light, Recommended, or Extreme mode, compare file sizes instantly, and download the result when attachments or uploads are too large.
Related
What is PDF compression?
The core goal of PDF compression is to reduce the file size while retaining the number of pages, format, and readability as much as possible, so that it can pass the size limit of email attachments, registration systems, or corporate forms. This tool uses qpdf-wasm to process locally in the browser and will not upload the file to the server.
Its working method is not to simply "remake a PDF", but to prioritize the organization of object streams, content streams and image resources to make the originally scattered or redundant data in the original file more compact. Extreme mode will further optimize image resources, so it is usually easier to obtain higher compression rates than light and recommended modes.
Compression effect is strongly related to file type. Scanned documents, screenshots, and PDFs with many pictures are often the easiest to shrink; PDFs with plain text, vector images, or optimized PDFs have limited compressible space, and sometimes they will only be slightly reduced, or even have almost no change.
PDF compression is usually suitable as a first step: first see if you can directly overcome the limit without changing the number of pages. If you actually only need to submit a few pages, are more concerned about the clarity of the source image, or the file is password protected, then deleting pages, splitting, compressing the image first, or decrypting it first is often more appropriate than repeated compression.
Use Cases
- PDF exceeds the limit as an email attachment and needs to be compressed before sending.
- Recruitment, registration, bidding or corporate forms limit the upload size and need to be slimmed down without changing the number of pages.
- The image PDFs of scanned contracts, document copies, quotations, etc. are too large, so I would like to try compressing them first.
- When sharing on mobile phones, instant messaging or cloud disk backup, you want to upload and download faster.
- Your resume, portfolio or job application attachment exceeds the recruitment system limit and you need to reduce the PDF size first.
- School applications, study abroad materials, and registration forms limit the size of single files. I want to preserve the formatting and compress them at the same time.
- Financial statements, invoice archives or audit attachments need to be uploaded to OA, ERP, reimbursement systems but the PDF is too large.
- When sending contracts, agreements, or quotations for legal, administrative, or procurement purposes, attachments that exceed the limit need to be compressed first.
- Before uploading scanned files, conference materials, and training manuals to the knowledge base or network disk, optimize the size first.
- Customers want to receive PDFs in WeChat, WeChat Enterprise, DingTalk or Slack, and hope that files can be transferred more easily.
- Send drawings, instructions, and brochures in a mobile network environment, hoping to reduce the upload waiting time.
- The PDFs exported by print shops, scanners or mobile phone scanning apps are too large in size, so I want to quickly slim them down before distributing them.
- When multiple departments collect documents, forms, and receipts, the PDFs submitted by each person need to be suppressed to a unified upper limit.
- Old documents only need to be lightly archived. We do not want to change the content or number of pages. We just want to reduce storage usage.
- When the site download center, help documents or product manuals provide PDF downloads to the outside world, we hope that the files will be smaller and open faster.
- You want to visually see the savings ratio before and after compression to determine whether the PDF is suitable for continued page deletion, splitting, or back-to-source processing.
How to Use
- Upload one PDF file or drag it into the drop zone.
- Start with Recommended mode. If the size does not drop enough, try Extreme; if you want the safest pass, use Light.
- Click “Compress PDF”, wait for the local process to finish, and review the before-and-after file sizes.
- Download the result. If it is still too large, switch modes and try again, or split/remove pages first.
Features
- Local in-browser processing: the file is compressed in your device memory with no server upload.
- Three compression modes: Light for a quick conservative pass, Recommended for most documents, and Extreme for more aggressive image and content-stream optimization.
- Drag-and-drop with instant feedback: see original size, compressed size, and saved percentage after processing.
- Designed to preserve document structure: page count, layout, selectable text layers, and links usually remain intact.
- No watermark download: get the compressed PDF immediately with no branding added.
When a PDF is too large, should it be compressed, deleted, split, or should the source file be processed first?
First, it depends on whether you want to keep the entire PDF, submit only some pages, send it in batches, or still keep the source image or document. The most trouble-free processing path for "file too large" caused by different reasons is different.
| Solutions | What situation is more suitable for | Advantages | limitations | Suggest next steps |
|---|---|---|---|---|
| Compress PDF directly | To preserve page count and layout, you only want to pass attachment or upload size limits first | The content is minimally changed and the number of pages is usually not changed, making it suitable for the first round of weight loss. | Compression space may be limited for plain text, vector graphics, or optimized files. | Use the "Recommended" mode first; if it still exceeds the limit, try "Extreme". If it is not enough, try deleting pages, splitting or source file processing routes.Compress PDF |
| Delete the page or extract the page first | In fact, you only need to submit a few pages, or you may want to remove the cover, appendices, and blank pages. | Directly reducing irrelevant content is often more effective than repeated compression, and is less likely to affect small words and details. | It will change the integrity of the document and is not suitable for scenarios where the entire document must be submitted as is. | First delete the number of pages you really want to deliver, and then determine whether you still need to continue compressing.Extract PDF pagesDelete PDF pages |
| Split into multiple PDFs | The platform allows multiple attachments, or very large files, which consume memory and take a long time to process in the browser. | It can reduce the size and processing pressure of a single file, especially suitable for scans with many chapters or very large ones. | It will turn into multiple files, and the management cost of the recipient will be higher. It is not suitable for platforms that only accept a single file. | After splitting by chapter, purpose or upload limit, compress each copy separately.Split PDF |
| Process the source image or document first | Scanned and screenshot-type PDFs are large, and you still have the original pictures, Word or PPT in your hands | With the ability to control image size, clarity, and export quality from the source, the results are often more controllable than post-compression. | The premise is to get the source file, which requires more steps than direct compression. | First compress the image or optimize the source document and then re-export the PDF; if the file has a password, decrypt it first and then continue processing.Image compressionPDF decryption |
Best Practices
Start with “Recommended” mode
Recommended mode is suitable for most ordinary documents. Only when the volume is still clearly beyond the limit, switching to extreme mode can reduce unnecessary fluctuations in image quality.
Keep original files when compression ratio is very low
Pure text, vector graphics or optimized PDFs have limited compression space. If the savings are small, it usually doesn't make sense to keep repeating the compression.
When the original image is still there, the source image will be processed first.
The size of a scanned or album-type PDF comes mainly from images. Compressing the source image first, resizing it, and then regenerating the PDF is often more stable than compressing it afterwards.
Image compressionCheck QR code, small print and signature after extreme mode
The more aggressive the image compression, the more likely it is to affect QR code scanning, thin-line tables, and small text. After downloading important files, open them for spot check first.
Change the processing order of large files or password files first
Very large PDFs can be split first and then compressed; PDFs with passwords can be decrypted first and then compressed. This makes it easier to succeed and more convenient to locate problems.
Split PDFPDF decryptionKeep an uncompressed original copy of important documents
For formal materials such as contracts, portfolios, and bidding documents, it is recommended to keep an original copy and then compress the copy. In this way, you can quickly roll back when the platform rejects it, the clarity is not enough, or it needs to be re-exported.
FAQ
Will compression make the PDF blurry or damage the text layer?
Usually not in a noticeable way. Light and Recommended are the safer choices; Extreme is better for image-heavy files. This tool focuses on structural and resource optimization, so selectable text layers and standard links usually remain intact.
Why did the file size barely change, or even become slightly larger?
Text-heavy, vector-based, or already compressed PDFs may have very little redundant data left. After structural rewriting, tiny size fluctuations can happen; if savings are minimal, keep the original file.
Is this tool good for scanned or image-heavy PDFs?
Yes. Those files usually shrink the most. If you still have the original images, resizing or compressing them before exporting the PDF can give you more predictable results.
Can I compress a password-protected or encrypted PDF directly?
Usually no. Remove the password protection with a PDF decrypt tool first, then come back to this page. If needed, you can encrypt the final file again before sharing.
Does the file get uploaded to a server?
No. The compression runs locally in your browser, so the file stays in your current device and browser memory instead of being sent to a remote server.
Does it support batch jobs or very large files?
This page handles one PDF at a time. Whether a huge file succeeds depends on browser and device memory; if the file is very large or the browser slows down, split it first and process the parts in a desktop browser.
Troubleshooting
After uploading, it prompts that the file is invalid or not a PDF.
Reason: The file may not be a valid PDF, or may have been damaged during downloading or exporting. Solution: First use a local reader to confirm whether it can be opened normally; if it cannot be opened, re-download or re-export the original file, and then come back to compress it.
When compressing, it prompts for password, protection or direct failure.
Reason: The file has password or permission restrictions, and the current compression process will not unlock the protected content for you. Solution: Go to /pdf/decrypt/ to decrypt first. After the compression is completed, if you still need protection, re-encrypt and distribute it.
The browser freezes, takes a long time, or compression fails
Reason: Very large PDFs take up more browser memory and CPU, especially documents with many scans or images. Solution: Close other large pages and use desktop browsers first; if the file is particularly large, split it first and then compress it one by one.
Still exceeds platform size limit after compression
Reason: The image PDF may still be too heavy, or the platform restrictions may be stricter than the compressed result. Solution: Prioritize deleting unnecessary pages, and split and submit if necessary; if the source image is still there, compress the image or re-export it and try again.
After the extreme mode, the QR code, small words or signature become unclear.
Reason: Extreme mode optimizes picture resources more radically, and the loss of details will be more obvious. Solution: Change back to the recommended or light mode and re-compress, and focus on checking the QR code, signature, thin-line form and small text after downloading.
The downloaded PDF cannot be opened or the preview is abnormal
Reason: The exception does not necessarily come from the compression itself, it may also be a problem with the original file structure or poor compatibility of some built-in previewers. Solution: Check with a desktop browser or professional PDF reader first; if the problem is still abnormal, use the recommended or light mode to recompress.
Glossary
- Object stream
- A PDF can pack many small objects into object streams to reduce overhead. Rebuilding object streams is a common structural optimization.
- Content stream
- Text, paths, and drawing commands on a PDF page are stored in content streams. Coalescing fragmented streams can reduce redundancy.
- qpdf
- A widely used PDF structure optimizer. This page's compression capability is built on the WebAssembly version of qpdf.
- Local processing
- The file is processed in your current browser and device memory instead of being uploaded to a remote server.
- Scanned PDF
- A PDF created from scans, photos, or screenshots where images dominate the file size. These files usually compress better.
How to choose between the three modes
Choose the mode based on file type and how much quality change you can tolerate.
| Mode | Best for | Notes |
|---|---|---|
Light | A quick conservative pass or when stability matters most | The least aggressive structural compression |
Recommended | Most everyday documents and upload-limit cases | Best balance of savings and stability |
Extreme | Scanned or image-heavy PDFs that must shrink more | Applies more aggressive resource optimization |
Expected results by PDF type
Compression results depend heavily on what is inside the file.
| PDF type | Typical behavior | Suggested next step |
|---|---|---|
Scans / many images | Usually the biggest size reduction | Start with Recommended, then try Extreme if needed |
Office-exported documents | Often a medium reduction | Optimize the source file first when possible |
Mostly text / vector graphics | Compression can be limited | Consider removing pages, splitting, or re-exporting |
Encrypted or already optimized | May fail or barely change | Decrypt first, or keep the original file |