Compress PDF Files

Most large PDFs are large because of images. A single phone photo can be 3 to 5 MB, and a scanned page saved at high resolution can be similar. Text on its own takes very little space.

Compression shrinks those images by lowering their resolution and storing them more efficiently. For reading on screen, 150 dpi is usually plenty. 300 dpi is the usual standard for print.

A quick test tells you what to expect. If you can select the text in your PDF, it is a digital document and may not shrink much. If you can't, it is a scan and usually shrinks a lot.

Common limits to aim for: 25 MB for Gmail, 20 MB for Outlook.com, often 10 MB for company mail servers, and 1 to 5 MB for many job portals, visa applications and university submission systems.

Compress once, from the original file. Compressing an already compressed PDF again gains little and can make images blurry.

If a PDF is still too big, split it. Extract the first half with Extract PDF Pages, then the second half, and send two smaller files.

Avoid the problem at the source when you can. When scanning text documents, choose 150 to 200 dpi and grayscale. In Word on Windows, the Save As PDF window has a Minimum size option for files meant for screens.

Open the compressed file and zoom in on the smallest text, signatures and stamps before you send it. If they are hard to read, go back to the original and use a lighter level.

Compression doesn't remove pages or change your wording. If the file contains pages nobody needs, deleting them with Remove Pages can save more space than compression.

Keep the original. If someone later asks for a print-quality copy, you can send that instead.