Know the limit and what counts toward it
Some mail systems cap the total message size; others cap individual attachments or apply separate sending and receiving limits. A file that fits by itself can still cause an error when combined with other files. Use a target comfortably below the published threshold.
For formal submissions, verify both the maximum file size and any accepted file types or page limits.
Understand what's inside the PDF
A text-based PDF can be small even with many pages, while a short scanned PDF may be large because every page contains a high-resolution photograph. Reducing JPEG-image quality helps only if the file contains compatible images that can be rewritten.
If there are no suitable images or the file is already optimized, do not expect dramatic size reductions.
Try the least destructive option first
Compress at a moderate quality setting and compare the output size with the source. Open the result and inspect pages with photographs, fine print and diagrams. Keep the original unchanged, especially if the PDF includes signatures, forms or accessibility structure.
Avoid repeated conversions through print-to-PDF and screenshots: they may remove searchable text and links or degrade document clarity.
When the target is not reached
A target-size field is an optional goal, not a promise. If normal optimization is insufficient, return to the source document and resize unnecessarily large embedded photos before generating a new PDF. For scanned documents, consider a lower scan resolution if detail remains legible.
If a recipient accepts a secure sharing link, that may be preferable to forcing excessive quality loss.
Verify before sending
Check page count, text selection, form fields, hyperlinks and orientation. For contracts and regulated documents, confirm whether edits invalidate signatures or other authenticity guarantees. Open the export in a second PDF reader when practical.
If the recipient cannot open the attachment, compatibility or document structure may matter more than the final number of megabytes.
A size-limit walkthrough
Imagine an email destination with a 10 MB attachment threshold and an 11.5 MB PDF. First inspect whether the document contains large photo scans. Try a moderate PDF optimization and compare the actual result. If the file remains above 10 MB, return to the original document and reduce embedded image size rather than repeatedly forcing lower quality.
The PDF diagnosis guide explains when compression produces almost no reduction. If your source document has high-resolution photographs, the image reduction guide may offer a safer starting point.
Document checklist before sending
Verify the page count, searchable text, embedded hyperlinks, orientation, form fields and signatures. A smaller PDF that changes the legal or practical meaning of its contents is not an acceptable export. Keep a copy of the original and, when possible, open the output in a second reader.
If the receiving system accepts a secure share link instead of an attachment, that option may preserve fidelity without needing further lossy transformations.