How to compress a PDF
- Add a PDF by clicking the dashed box or dragging the file onto it.
- Press Compress PDF. The file is re-saved in your browser, usually within seconds.
- Read the result line. It shows the original size, the new size and the change in percent. A minus sign means the file got smaller; a plus sign means the re-saved copy is larger.
- Download
compressed.pdfif it is smaller. If not, keep your original and look at the alternatives further down.
What this compressor does – and what it does not
A PDF is a collection of numbered objects: page descriptions, fonts, images and many small dictionaries that tie them together, plus a cross-reference table that records where each object sits in the file. Since PDF version 1.5, small objects can be packed together into object streams and compressed as a group, and the cross-reference table itself can be stored compressed.
This tool loads your file with the open-source pdf-lib library and writes a fresh copy with object streams switched on. The rewrite also drops outdated versions of objects that pile up when a file is edited and saved incrementally many times, because only the latest version of each object is kept.
It does not resample or re-encode images, remove or subset fonts, or strip metadata and attachments. Everything that is drawn on the page stays byte-for-byte the same, so the result is lossless: pages look identical. The flip side is that savings depend entirely on how the file was made.
| Kind of PDF | What to expect here | Better route if it is not enough |
|---|---|---|
| Text documents from older software, forms, files edited and re-saved many times | Often a useful reduction | Split off pages you do not need |
| Recent exports from office suites | Little change, sometimes slightly larger | Re-export with smaller images |
| Scanned documents | Almost no change – nearly all bytes are image data | Rescan or re-encode images at lower resolution |
| Photo-heavy brochures and slides | Little change | Re-export with image downsampling |
Tips for getting a smaller file
- Start from the source. In Microsoft Word, choose Save As → PDF and select "Minimum size (publishing online)". In LibreOffice, use Export as PDF and enable "Reduce image resolution" with a lower JPEG quality.
- Scan smarter. Text documents are perfectly readable at 200 DPI in grayscale; a 600 DPI color scan of the same page holds many times more pixels.
- Remove pages first. Appendices, blank pages and duplicate scans can go with Split PDF before you compress.
- One pass is enough. Running the result through the tool again gains nothing – there is nothing left to pack.
When it is worth a try
- A long report or contract that has been edited and saved many times.
- A form or text-heavy file that is just over an upload portal's limit.
- A quick check whether a file can shrink without any loss of quality before you reach for lossy methods.
Limitations and alternatives
- Images are not downsampled. For scans and image-heavy files, use a tool that re-encodes images. Ghostscript is free:
gs -sDEVICE=pdfwrite -dPDFSETTINGS=/ebook -o out.pdf in.pdf(/screentargets about 72 DPI images,/ebookabout 150 DPI,/printerabout 300 DPI). On a Mac, Preview's File → Export with the "Reduce File Size" Quartz filter is quick but can make images very blurry. - A lossy route with PDF Hut: convert scanned pages with PDF to JPG at 1x or 2x and rebuild them with JPG to PDF. Only do this for scans – any real text becomes a picture and can no longer be searched or copied.
- Password-protected PDFs are not supported; the output of an encrypted file may not open.
- Digital signatures are invalidated by any rewrite of the file, including this one. Compress before signing, never after.
- pdf-lib records itself as the file's "Producer" and updates the modification date; other document properties are kept.
Frequently asked questions
Why is my compressed PDF the same size or bigger?
The file was probably already saved with compressed object streams, or most of its size is image data, which this tool does not re-encode. In that case keep the original and try the alternatives on this page.
Does compressing reduce the quality of my PDF?
No. The tool only repacks the file's internal structure. Text, fonts and images are left exactly as they were, so every page looks the same.
How much smaller will my file get?
It depends on how the PDF was produced. Files edited many times or made by older software can shrink noticeably, while modern exports and scans change very little. The result line shows the exact change in seconds.
Can I compress a scanned PDF here?
You can try, but expect little change because nearly all of a scan is image data. Rescanning at a lower resolution or re-encoding the images with a tool such as Ghostscript works much better.
Will compressing break a digital signature?
Yes. Any tool that rewrites a signed PDF invalidates the signature, so compress documents before they are signed.
Is my file uploaded to a server?
No. The file is read and re-saved by pdf-lib inside your browser, and the result is created on your device.
Related tools
- Split PDFSend only the pages that matter to get under a size limit.
- PDF to JPGRender scanned pages as smaller images.
- JPG to PDFRebuild a PDF from those images.
- Merge PDFCombine the parts again after trimming them.
Further reading: How to make a PDF small enough to email.