· 7 min read
How to compress a large PDF so it actually sends
Gmail rejects attachments over 25 MB, most corporate mail servers stop at 10 MB, and plenty of upload forms cap at 5 MB. Meanwhile a scanned twelve-page contract can easily be 40 MB. The fix is rarely a single button — it is a short sequence of checks.
Step 1 — find out what is making it big
Open the PDF and try to select a sentence with your cursor. If you can, the pages are real text and the file should already be small — a large size then usually means embedded images or fonts. If you cannot select anything, every page is a photograph, and images are your problem.
Step 2 — compress at the right level
- Open the Compress PDF tool and add your file.
- Start with the Recommended level. It targets the balance most email attachments need.
- Read the reported before and after size. If it is still too big, try Maximum; if the text has gone soft, drop back to Basic.
- Download and open the result at 100% zoom to judge readability honestly.
Compression here re-renders each page as an image, so selectable text and clickable links are lost. Keep the original file — treat the compressed copy as the version you send.
Step 3 — if compression is not enough
- Split the document. Use Split PDF to send chapters or sections as separate, smaller attachments.
- Remove pages you do not need to send at all — blank scanner pages and duplicate cover sheets are common.
- Share a link instead. For anything over about 25 MB, a cloud link is faster and more reliable than an attachment.
Prevent it next time
If you control the scanner, scan at 200–300 dpi in greyscale rather than 600 dpi colour. That single change routinely cuts file size by 80% with no meaningful loss for text documents. When exporting from Word or design software, choose the 'smallest file size' or 'web' preset unless the document is going to a commercial printer.
One warning worth repeating: never compress the only copy of a legal, medical or archival document. Compression is lossy, and there is no way back.