Compress PDF for email — the 5 MB problem
Gmail caps you at 25 MB. Some corporate gateways cap you at 5 MB. Here's how to land just under any cap without making the file look like a fax.
Bouncing PDFs because they're too big to email is the dumbest tax we pay on modern work. The fix is 30 seconds. Knowing how to do it right saves you a 'can you re-send that smaller?' email and the half-day delay it adds.
Pick a target, not a level
Most compress tools ask you to pick Light/Balanced/Strong, and then you guess. The smarter mental model: pick a target SIZE first ('under 5 MB', 'under 24 MB for Gmail'), then choose the gentlest level that gets you there. We don't yet ship a built-in compress tool ourselves (pdf-lib doesn't support compression; we're building a server-side qpdf+ghostscript pipeline) — until then, Adobe Acrobat Online's free tier or iLovePDF's compress will get you to a target size.
Why email caps vary
Gmail caps at 25 MB, Outlook 365 ranges 20-35 MB depending on tenant config, government and bank gateways often cap at 5-10 MB. Each cap is per-message including all attachments — a 24 MB compressed PDF leaves room for the message itself but not for additional files.
Pitfalls
Don't compress twice — each pass re-encodes already-compressed JPEGs, compounding artifacts. Don't use Strong on print-bound documents — 150 DPI is fine on screen but soft on paper. Don't compress signed PDFs — compression rewrites the byte layout and voids cryptographic signatures.
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