How to actually get a PDF under an attachment limit

An email system says 25 MB, a portal says 10 MB, and you have a 31 MB PDF. The instinct is to compress harder. Sometimes that is right, and often it is the wrong first move.

First, work out what is actually big

Open the file and look at the page count and the page types. A 30 MB, four-page document is almost certainly a handful of enormous scanned images. A 30 MB, 300-page document is probably structural overhead and duplicated assets. Those need opposite treatments.

The ladder, in order

1. Strip the metadata. Instant, invisible, and it sometimes removes a surprising amount.
2. Run structural compression. See how far that gets you — it is the only step with no downside.
3. If the limit is per file, split the document. A reader can usually cope with two attachments; nobody can cope with an unreadable file.
4. If only certain pages are needed, extract just those instead of shipping the whole thing.
5. Only then consider reducing quality — and if the document is a scan, re-scan instead of squeezing a JPEG that is already compressed.

Verify before you send

• Check the actual byte size, not what your file manager rounds it to.
• Open the result and confirm the page count matches what you expect.
• Select and copy some text to confirm it is still text.
• Check the pages that matter most — a compressed page 30 often looks worse than page 3, and that is where people give up.

Why compression is usually not the answer

Most large PDFs are large for a structural reason that has nothing to do with content: duplicated images, embedded fonts nobody uses, colour profiles, incremental save histories. None of that is visible on the page, and removing it costs nothing in quality. That is why structural compression is worth trying before anything else — and why a file that resists it is usually telling you something useful about its contents.