Compress PDF

Compress PDF rewrites a file with object streams. It does not resample photos, so an already-compressed PDF may not shrink. Each upload can be up to 25 MB.

Worked example

scan-image.pdf is one page, a JPEG photograph, at 2,454,893 bytes. Run Compress PDF finished in 74 ms. The download 1792694082879-compressed-scan.pdf was also 2,454,893 bytes, a change of 0. The same pass on split-six.pdf, a six-page text file of 1,910 bytes, wrote 1792694081599-compressed-text.pdf at 1,914 bytes in 10 ms, so that file grew by 4 bytes. Saving the text file once with object streams and running the job again left it at 1,914 bytes and took 3 ms. There is no screen, ebook, or print preset, so those byte counts are the whole result. Keep the original beside the download if you might print the scan later, because this rewrite is not a quality choice.

When it fails or surprises you

Already-compressed files may not shrink. The photo page stayed at 2,454,893 bytes. The text page grew from 1,910 bytes to 1,914. A nine-page file made by repeating that photo was 22,089,061 bytes, near the cap, and the rewrite was 22,089,064 bytes, 3 bytes larger, in 1,025 ms. protected.pdf is not rejected. The loader uses ignoreEncryption, and the save went from 1,251 bytes to 1,244 bytes in 7 ms. Opening that output without ignoring encryption still says the file is encrypted, so the password remains. A 27,262,976-byte upload shows Internal server error.

What reduce PDF file size means here

Object streams pack PDF objects. They do not decode the JPEG inside a scan, and there is no quality control to trade sharpness for bytes. A phone scan that is already one image per page can come back the same size, which is what the 2,454,893-byte page did. The download is a new file, and the original on your computer is not replaced. Compare the two sizes before you discard the master. If the attachment must be smaller, remove pages first. A second click on a file that already uses object streams did not help the text sample. Next step to drop pages: /tool/split-pdf. Next step to join files without expecting them to shrink: /tool/merge-pdf.