Outlook.com PDF Attachment Limit: 25 MB
Direct answer
Outlook.com's per-message limit, the PDF size that leaves room for encoding, and what to do when a file is still too big.
Why this matters: BytesPDF processes the file on your device and does not send it to a compression server. Delivery by email or portal is a separate step.
Outlook.com (formerly Hotmail) lists a 25 MB limit per message. Base64 encoding makes the transmitted attachment larger than the file on disk, so a PDF close to 25 MB can still fail. Plan around the safe size below and send a OneDrive link for larger files.
PDF Compression Core
Recompress supported PDF images locally with an adjustable quality and size trade-off.
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PDF files only · Max 150MB per file · Up to 10 at a time
Limits
Outlook.com Limits and Safe Sizes
Use these checkpoints with the destination's current instructions. Requirements can vary by account, institution, region, document type, and workflow. BytesPDF does not verify or guarantee recipient acceptance. Page reviewed . See the browser-local processing architecture.
| Portal / Recipient | Requirement / check |
|---|---|
| Per-message limit | 25 MB, measured after encoding |
| Safe PDF size on disk | About 18 MB |
| Larger files | Send as a OneDrive link |
| Recipient's provider | Their inbound limit can be lower |
Trade-offs
Which Compression Mode Should You Pick?
Three modes — pick based on what the recipient needs to do with the file.
✅ Text documents
Usually the best candidates. Check the result before sending.
🟡 Scans and photographs
Expect softer detail. Compare with the original.
🟡 Digitally signed or fillable forms
A digitally signed file is not compressed, because compressing it would break the signature. Check form fields in the output before sending.
Before compressing a high-stakes document
Compression rewrites the PDF. BytesPDF rejects files containing a cryptographic signature because any rewrite would invalidate it. Keep digitally signed files and required PDF/A archival masters unchanged. Bookmarks, links, forms, annotations, accessibility tags, and color profiles are preserved where the PDF library can retain them, but always inspect the downloaded copy before filing or submitting it.
What is the attachment limit for Outlook.com?
How do I send a PDF larger than 25 MB from Outlook.com?
Does compressing a PDF to 18 MB guarantee delivery?
Ready to get under the limit?
Drop your file in — the compressor runs in this tab, so nothing is uploaded. Outlook.com's per-message limit, the PDF size that leaves room for encoding, and what to do when a file is still too big.
No account · No signup · No watermark · No PDF upload
Editorial review: Limits come from the BytesPDF guides linked on this page and were checked on October 15, 2026. Mail and portal rules change, so confirm the current limit on your account.
Last reviewed: . We update this page when provider guidance or tool behavior changes.
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Limits and examples are informational and may vary. Confirm the recipient's current requirements before submitting a high-stakes document. Digitally signed or archival-conformance files should be submitted in their original form.