Make a PDF Under 20MB (Outlook)
Outlook often enforces a 20 MB attachment limit. Use these steps to compress or split your PDF so it sends reliably.
Step 1: Start with the Outlook preset
Choose the Outlook 20 MB preset to target the typical attachment limit.
PDFThin optimizes first, keeping layout intact when possible.
Step 2: Adjust for strict systems
Some corporate systems are stricter than Outlook. If you see errors, lower the target to 18-19 MB.
Smaller targets also leave room for additional attachments.
Step 3: Split oversized PDFs
If a single file still cannot fit, use Split by size to generate multiple parts under 20 MB. Attach the parts in order and mention how many parts are included.Step 4: Send with confidence
Verify the file size before sending to avoid Outlook errors.
If you continue to see issues, reduce the target and retry.
FAQ
Is Outlook.com limited to 20 MB?
Outlook.com allows 25 MB, but Outlook desktop often uses 20 MB. Use the stricter limit for safety.
Why does a 19 MB PDF still fail?
Encoding overhead or other attachments can push the message over the limit. Try an even smaller target.
Can I attach multiple parts?
Yes. Attach the parts in order or send multiple emails if needed.
Outlook best practices
Use a safety margin
Targeting 18-19 MB avoids surprises when Outlook applies encoding overhead.
This is especially helpful when sending multiple PDFs.
Explain the split
If you send multiple parts, include a short note so recipients know the order.
Clear instructions reduce back-and-forth and speed up review.