Compress PDF — Free, Fast & Private
This compresses a PDF the way a PDF compressor built on a browser can: it renders every page, re-encodes each one as a JPEG at the quality you chose, and rebuilds the document around them. One file in, one file out, nothing uploaded. A 10 MB scan of a certificate set typically comes back at 1-3 MB.
The trade-off is real and worth stating before you start. Rebuilding this way rasterises the whole document, so any selectable text becomes part of the page image. Text stops being searchable and copyable, and the file will not pass a portal that requires machine-readable text. For a scanned document that was already an image, you lose nothing. For an exported report or a contract with live text, do not use this route — export it again at a lower image quality from whatever produced it. The tool checks the first few pages for live text when you choose the file and warns you before you commit, rather than after.
Page geometry survives exactly. An A4 page goes in at 595.28 × 841.89 pt and comes back at 595.28 × 841.89 pt, not a rounded approximation and not the 2.7×-inflated page this round trip used to produce before v4.33.0. That matters if you are going to print the result, or submit it somewhere that validates A4. Resolution is what you are trading away; page geometry is not.
It can also lose, and it says so when it does. Photographing a page of sharp text costs more bytes than the instructions for drawing that text did, so a born-digital document can come back bigger than it went in. When the finished file is measured and turns out not to be smaller, you are shown both numbers and given nothing to download. Keeping your original is the correct outcome in that case, and handing you a larger file under a Compress heading would not be.
Everything runs in your browser using PDF.js to render and jsPDF to rebuild. Your documents never leave your device, which is the point for legal contracts, financial statements, medical records, and ID paperwork.
Most email services cap attachments at 25 MB, and many form portals want PDFs under 5 MB or 2 MB. If you need to land under a specific kilobyte number rather than just smaller, the size-targeted PDF builder aims at a byte budget instead.