How to shrink a PDF for email
Attachment limits, what actually makes a PDF large, and which compression method to use for scans, text documents and image-heavy reports.
Updated 2026-08-03
Almost every "compress PDF" search starts with a bounced email. The limits are lower than people expect and they apply to the encoded message, not the raw file — which is why a 24MB attachment fails a 25MB limit. Here is what the limits actually are, what makes a PDF heavy, and which fix applies to which kind of document.
What the attachment limits actually are
Base64 encoding inflates an attachment by roughly 33%, and every provider applies its limit after that step. The practical ceiling is therefore about three-quarters of the advertised number.
| Service | Stated limit | Realistic file size | Notes |
|---|---|---|---|
| Gmail | 25 MB | ~18 MB | Larger files are auto-converted to a Drive link |
| Outlook / Microsoft 365 | 20 MB (web), 150 MB (desktop, configurable) | ~15 MB | The recipient server usually decides |
| Yahoo Mail | 25 MB | ~18 MB | |
| iCloud Mail | 20 MB | ~15 MB | Mail Drop handles up to 5 GB separately |
| Most corporate servers | 10 MB | ~7 MB | The most common real-world limit, and the one that bites |
Work out what is making it big
A PDF is heavy for exactly one of three reasons, and the fix differs completely between them. Check the page count and whether there is a text layer before compressing anything.
- Scanned pages. Every page is a photograph. A 20-page color scan at 600 DPI is routinely 40–80 MB. This compresses dramatically — 80–95% is normal.
- Embedded photographs. A report with 30 full-resolution phone photos carries 30 × 3–5 MB. Compresses very well.
- Text and vector graphics only. Typically under 1 MB already. This barely compresses, and rasterizing it makes things worse while destroying the text layer.
Pick the right fix
| What you have | What to do | Typical result |
|---|---|---|
| A color scan | Compress at medium resolution, 60–70% quality, grayscale on | 80–95% smaller |
| A photo-heavy report | Compress at medium resolution, 70% quality | 60–85% smaller |
| A text document already under 2 MB | Nothing — send it as is | Compression will make it larger |
| One long document, still too big | Split it and send in parts | Proportional |
| A document only some of which is needed | Extract the pages that matter | Proportional |
The trade-off nobody mentions
Rasterizing compression — which is how essentially every online PDF compressor works, including this one — replaces the text layer with a picture of the text. The result looks identical and is far smaller, but it is no longer selectable, searchable, or readable by a screen reader. For a scan that never had a text layer, you lose nothing. For a contract someone needs to search, keep the original and send that instead.
Questions
Why is my PDF still too big after compressing?
Either it was already efficient — a text-only PDF has almost nothing to squeeze — or it is simply very long. Check the page count first. A 400-page document at 100 KB per page is 40 MB no matter what you do, and splitting is the only real answer.
Does compressing a PDF reduce its print quality?
Yes, measurably, if you print it. At medium resolution a page is rendered at about 144 DPI, which looks fine on screen and slightly soft on paper. If the file is going to a print shop, send the original.
Is it safe to compress a confidential PDF online?
On most sites, no — your document is uploaded to their server and processed there. On DuckyTools the work happens in your browser, so the file never leaves your device. That distinction matters most for exactly the documents people most often need to compress: contracts, medical records and financial statements.