What to do when a PDF is too large to email

The limit is smaller than the number you were told

Most mail providers advertise a limit of around 25 MB, and most people discover the hard way that a 24 MB file still bounces. Two things account for the gap.

Attachments are encoded, not sent raw. Email carries binary data as base64 text, which is roughly 33% larger than the bytes it represents. A 20 MB PDF arrives at the server as about 27 MB of message. That single fact explains most rejections just under the stated limit.

The limit that matters is the smallest one on the path. Your provider, the recipient's provider and any corporate gateway in between each have their own, and the message has to satisfy all of them. Corporate servers commonly sit at 10 MB, sometimes 5 MB, and they are frequently the one that refuses.

A practical target: get under 10 MB for general use and under 5 MB if you know the recipient is on a company system. Compress to 1 MB and compress to 500KB exist for the stricter cases, such as upload forms that name a number.

The order to try things

1. Compress. Compress PDF re-encodes the images, which is where the size almost always is. Text and vector graphics are already tiny by comparison — a 200-page text document is often under 2 MB, while one photograph can be 4 MB on its own.
2. Check what you got. Compression is lossy: it trades image detail for size. Open the result and look at the pages that matter before you send it.
3. Split, if it is still too large. Split PDF by size lets you name a limit and get pieces that each stay under it. Bear in mind the parts can add up to more than the whole, because each file needs its own copy of the fonts and images its pages use.
4. Send only what is needed. Often the recipient wants four pages of a ninety-page report. Extract pages is both the smallest file and the more considerate message.

If compression barely moves the file, the reason is usually structural rather than a failure of the tool — why some PDFs will not get any smaller covers the cases.

When not to attach it at all

Some documents should not be email attachments regardless of size. A 60 MB scanned archive compressed to 9 MB is technically sendable and still a poor thing to put in someone's inbox, where it will sit in their storage quota forever and be impossible to update.

A link to shared storage is better for anything large, anything that will be revised, or anything going to several people. It also gives you something an attachment never does: the ability to correct a mistake after sending.

One caution if you switch to a link. An attachment goes to the people you addressed it to; a link goes to whoever has the link. If the document contains anything sensitive, check the sharing settings rather than assuming them, and consider whether the file itself should carry a password — what a PDF password actually protects is worth reading first, because the answer is narrower than most people expect.