Compress PDF online

How to compress a PDF

1. Choose a PDF file.
2. Click Compress PDF.
3. Check the before-and-after size shown in the result.
4. Download the compressed file if the size reduction is useful.
5. If the reduction is small or zero, read the limitations section below before trying another tool.

This tool cannot re-compress the images embedded inside a PDF the way the image compressor re-encodes a JPG or PNG. It rebuilds the PDF's internal object structure, which mainly helps files that were saved without object streams or that contain redundant internal objects.

What this does and how it works, honestly

A PDF file is not just page content; it also contains an internal structure of objects (fonts, images, page descriptions, cross-reference tables) that describe how everything fits together. This tool reloads the PDF and re-saves it with object streams enabled, which groups many small internal objects together and compresses them, instead of storing each one separately and uncompressed. For PDFs originally created by software that didn't use this optimization (common with some export tools and older software), this can meaningfully shrink the file. For PDFs that were already saved efficiently, or whose size mostly comes from large embedded images rather than structural overhead, the size reduction can be small or close to zero.

Why this is not like the image compressor

The site's image compressor reduces file size by re-encoding pixel data at a lower quality, which reliably produces a much smaller file because JPG quality is a direct, adjustable tradeoff. A PDF's file size is often dominated by embedded images that were already compressed when they were placed into the PDF; safely re-compressing those images further would require decoding, re-encoding, and re-embedding every image inside the PDF at a chosen quality level, which is a fundamentally different and much heavier operation than the structural optimization this tool performs. Being upfront about this distinction matters: a "PDF compressor" that always promises dramatic size reductions on any file is usually either doing lossy image re-compression (with a real quality cost that should be disclosed) or overstating what it did.

Best practices

• Try it first on files exported from older or less common software, where the biggest gains are more likely.
• Check the before-and-after size shown after compressing rather than assuming a reduction happened.
• If the file is large because of high-resolution scanned images, consider whether a lower-resolution re-scan, or converting pages to JPG with the PDF to JPG tool at a smaller size and rebuilding, is a better fit for your specific goal.

Common mistakes to avoid

• Expecting the same kind of size drop you'd get from compressing a JPG photo. This tool doesn't touch embedded image data at all.
• Running it repeatedly on the same file expecting further gains. Once a PDF is saved with object streams, re-running this tool again produces no further meaningful change.
• Assuming a 0% result means the tool failed. It means the file was already reasonably efficient internally; this is expected and honestly reported, not an error.

Real-world use cases

• Shrinking a PDF exported from older desktop software before emailing it.
• Cleaning up a PDF that was edited and re-saved many times, which can accumulate redundant internal objects.
• A quick first attempt before deciding whether a heavier approach (like re-scanning at lower resolution) is worth the effort.

Supported formats

Input: a single standard, non-encrypted PDF file. Output: the same PDF content, restructured internally for potentially smaller file size. Page count, page content, and visual appearance are unchanged; only the internal storage efficiency is affected.

Worked example: two very different starting points

Results vary enormously by source file, which is exactly why this tool reports the specific before-and-after size rather than a promised percentage. Two realistic outcomes:

Limitations

This tool cannot open password-protected or encrypted PDFs. It does not re-compress embedded images, does not reduce image resolution, does not remove embedded fonts, and does not strip unused objects beyond what standard object-stream saving achieves. If your specific goal is the smallest possible file size regardless of image quality, this tool alone may not get you there; there is currently no lossy image-recompression option for PDFs on this site.

Privacy

Your PDF is read and re-saved locally in your browser using the pdf-lib JavaScript library loaded from this site. Files are not uploaded to a server. See the privacy policy for full detail.

Troubleshooting

• If the result shows little or no size reduction, the file was likely already saved efficiently; this is expected, not a failure.
• If you need a smaller file regardless, consider whether the file's large images could be reduced before they were placed into the PDF, or convert pages to JPG at a smaller size with PDF to JPG.
• If compressing fails, the file may be password-protected; this tool cannot open encrypted PDFs.

Conclusion

Use this tool as a quick, honest first attempt at shrinking a PDF's file size, understanding that the result depends heavily on how the file was originally created. For actual image-quality tradeoffs, the site's image compressor handles individual photos and screenshots with real, adjustable quality control.