Compress PDF
Reduce the size of a PDF by choosing the compression level. Ideal for scanned, image-heavy documents. Everything runs in your browser.
One PDF file
How it works
The tool redraws each page as a lower-quality image and rebuilds the PDF: it's the most effective way to shrink scanned or photo-heavy documents, which are almost always the heaviest. Start with Medium and move to Strong only if you need a much lighter file.
An important note
Because the pages become images, in the compressed PDF the text will no longer be selectable or searchable. If your PDF is text-only it's already very light and this kind of compression isn't worth it: it's meant mainly for scans and image-heavy documents. If the file is still over the portal's limit even after compressing, you can break it up with Split a PDF by size.
Where the size is, almost always
In a heavy PDF ninety per cent of the space is in the images, not the text: a thousand pages of plain text fit in a few megabytes, a single colour scan at 600 dpi takes five. Compressing a PDF therefore means, nearly always, recompressing its images.
The other heavy item is embedded fonts: if every part of a composite document brings its own, you reach several megabytes of typefaces alone. It is why a file born from merging twenty documents weighs more than the sum of its pages.
The number that counts is dpi, not quality
Lowering JPEG «quality» gains less than people think; the real saving comes from reducing resolution. A scan at 600 dpi holds four times the pixels of the same page at 300, and 300 dpi is already more than enough to print a text document.
There are three practical thresholds: 300 dpi for printing, 150 dpi for reading on screen or emailing, 72 dpi for a preview only. Going below 150 on a document with scanned text makes it tiring to read and useless for character recognition.
When compressing is pointless
If the PDF is made of real text and not scans, compressing gains almost nothing, because text is already compressed and takes very little. A 300 kB file of pure text pages is already at its minimum.
And if the document is to be archived or sent to a printing house, compressing is exactly what not to do: compression is irreversible, and a reduced image cannot be brought back. In that case you keep the original and compress only the copy you send.
Nearby tools
If the limit to respect is a precise one, Split a PDF by size makes parts already under the threshold. For Office files the equivalent is Compress an Office file, and for images alone Compress image.