The short answer
Compress the PDF to a size comfortably under your provider’s limit — under 18 MB for a 25 MB cap, because attachments grow by about a third in transit. If the quality has to stay exactly as it is, split the file into parts instead.
Step by step
- Find out the real limit Gmail and most Microsoft 365 mailboxes stop at 25 MB, Outlook.com and iCloud at 20 MB, and plenty of company gateways at 10 MB. Aim below it, not at it.
- Compress to a target Open Compress PDF, type the size you need and run it. Scans and photo-heavy reports usually drop by 80–95% with nothing visible lost.
- Look at the before-and-after The result shows both versions of a page under a divider, with a score for what changed. Check the page with the smallest print.
- If it still will not fit, split it Split by size fills each part to just under the limit, so you send as few attachments as possible. Name them "1 of 3" in the email.
- Attach and send The compressed file is an ordinary PDF: same pages, same order, text still selectable and searchable.
Questions
Why did a 24 MB file bounce from a 25 MB limit?
Attachments are encoded for transit, which adds roughly a third to their size. Keep the file under about 18 MB for a 25 MB limit.
Does zipping help?
Barely — PDF streams are already compressed. Zip to bundle several files into one attachment, not to shrink one.
Will the recipient notice the compression?
On a text document, no: the text layer is untouched. On a photo-heavy file, check the preview at the target size before sending.
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