A PDF can exceed the receiving mail system's attachment limit. Check that limit first, then inspect a smaller copy before attaching it.
Attachment limits vary between services and organisations, and message encoding adds overhead. Check the recipient's actual limit and leave room below it. An approved sharing link is an alternative, but uploading elsewhere changes who can access the file.
All three presets turn pages into images, removing selectable text and interactive form behaviour. Existing certificate-based signatures are not preserved.
Output size is not guaranteed. There is no exact-KB control or result preview; download and inspect the saved PDF.
Email turns an attachment into text before it travels, which makes it about a third bigger. A 20 MB file can therefore be refused by a mailbox that advertises a 25 MB limit. Aim to end up well under the stated limit, not just on it.
If the document is still too big at Balanced, you do not have to go to Smallest straight away. Splitting the file and sending it in two emails keeps the text sharp. Another option is to put the file in cloud storage and send a link instead of the file.
Keep the original or re-export from its authoring app with smaller embedded images. Gentle also rasterises text; Brodidit has no text-preserving PDF compression mode.
A file that needs a password to open must be unlocked first with Protect PDF. If a very large merge runs out of memory, join the files in two stages and then join the two results.
Email encodes attachments, and that makes them roughly a third larger than the file on your disk. Keep the file comfortably under the limit.