How to compress a PDF for email without wrecking quality
Updated 13 August 2026
Compress the PDF in your browser before attaching: Balanced mode keeps text selectable and reports the real saving. The verified caps: Gmail allows 25MB per message, Outlook.com 25MB per attachment, and desktop Outlook defaults to 20MB for internet mail accounts — corporate servers often allow less.
Fit a PDF under email limits free in your browser — Gmail allows 25MB, Outlook.com 25MB, desktop Outlook defaults to 20MB. No upload.
UnboundPDF is a free suite of 53 PDF and image tools that run entirely in your browser — merge, split, compress, edit text, OCR in 126 languages, redact, sign, convert and archive to PDF/A. Your document is read and written by the page on your own device; there is no document-upload endpoint in the core tools, no account, no watermark and no daily cap. Every result can be checked — with the Network tab, or with the Document Passport the Workspace writes for a chain of steps.
- Open Compress PDF and add your file.
- Pick Balanced to hit a size target with the least quality loss — text stays selectable.
- Or pick Maximum if you need the smallest file and can accept pages as images.
- Compress, compare the before/after sizes, then download.
Balanced requantises photos in the JPEG coefficient domain when possible — it does not decode and re-encode every image for a generation loss.
How the two modes decide what to shrink
Most of a heavy PDF is images. Balanced re-encodes those while leaving text, fonts and vector graphics alone — a compressed contract still has real, selectable text, and headings do not blur. Maximum goes further: pages become images, which is the smallest output but gives up selectable text. Choose Maximum only when the size cap matters more than being able to copy from the file.
The real limits, from the providers themselves
| Provider | Documented limit | Source, checked Aug 2026 |
|---|---|---|
| Gmail (personal) | 25 MB per message | Google's own help pages |
| Outlook.com | 25 MB per attachment | Microsoft's sending-limits page |
| Outlook desktop (internet mail) | 20 MB default | Microsoft's Outlook documentation |
| Work/school accounts | set by the administrator — often 10 MB | provider admin docs |
Transport encoding inflates attachments by roughly a third, so treat the stated number as a ceiling, not a target. Compress with Balanced first and check the reported saving; reach for Maximum only if a scan still misses the cap. If one file must cross several mails anyway, Split by Size produces parts under a size you set. Measured example, 13 Aug 2026: a 784 KB scan came out of Balanced at 418 KB and Maximum at 238 KB — real result-panel numbers, and the same run pattern applies at megabyte scale. Tighter caps than email? See under 1MB, 500KB and 100KB; portals with their own rules are covered in the government-portals guide.
When the file will not shrink
Some PDFs are already lean — a document that is mostly text has nothing heavy to re-encode, and the tool reports the real saving instead of faking a reduction. A file that is one big scanned image trades size against legibility: below a point, stamps and signatures stop being readable, which matters if the recipient must verify them.
Attachments are the leak, not the tool
The file you are compressing is usually about to be shared — which is exactly when you do not want an extra copy sitting on a compression service’s server. This one runs in your browser; prove it with the Network-tab method in the PDF Privacy Lab.
Frequently asked questions
What is the attachment size limit for Gmail and Outlook?
From the providers' own documentation, checked August 2026: Gmail personal accounts allow 25MB per message; Outlook.com allows 25MB per attachment; desktop Outlook defaults to 20MB on internet mail accounts. Work and school accounts can be set lower by administrators.
Why does my email bounce below the stated limit?
Attachments are re-encoded for transport, which inflates them by roughly a third, and corporate gateways impose their own caps on top. Aim well under the stated number — a 25MB limit is comfortable for attachments up to about 18MB.
Will compressing keep the text selectable?
In Balanced mode, yes — it re-compresses only the images inside the file and leaves text and vectors untouched. Maximum mode re-renders pages as images: smallest result, right for scans, wrong for contracts you want searchable at the other end.
Is my PDF uploaded somewhere to be compressed?
No. The work happens in your browser on your own device — which matters precisely because the file is about to be shared. You can watch the Network tab while it runs and see that no request carries your document.