How to Reduce PDF File Size for Email
Most email services reject attachments over about 25 MB, and plenty of company mail servers cut that to 10 MB. A PDF that was fine on your desktop bounces the moment you try to send it. Here is how to work out why it is big and what actually shrinks it.
First, find out what is making it big
PDFs get large for one of three reasons, and the fix is different for each.
- Scanned pages. Each page is a photograph. A 20-page scan at 300 dpi in colour can easily be 40 MB. This is the most common cause by far.
- Embedded photographs. A report with a dozen full-page images from a modern phone camera carries a dozen 4 MB files inside it.
- Embedded fonts and vector graphics. Rarely a problem — a text-heavy document of 200 pages is usually only a few megabytes.
Quick test: open the PDF and try to select a sentence with your cursor. If the text highlights, it is a real text document. If nothing happens, every page is an image, and that is where the size is going.
Compressing a scanned or image-heavy PDF
The effective approach is to re-encode each page at a lower quality. On a scan this typically cuts the file by 60 to 90 per cent with no meaningful loss in readability, because the fine detail being discarded is scanner noise rather than information.
Start on the recommended setting. If it is still too big, go to strong. If the text starts looking soft, go back a level and instead reduce the page count or split the document.
The trade-off is worth stating plainly: because pages become images, text in the result is no longer selectable or searchable. For a scan that was already images, you lose nothing. For a text document, you lose something real — which is why the tool warns you when compression made the file bigger rather than smaller.
When splitting beats compressing
If the recipient only needs part of the document, sending 8 pages instead of 60 is better than sending a degraded version of all 60. It is also faster for them to read.
If you built the PDF yourself
The cheapest fix is upstream. If you are creating the PDF from photos, compress the images before they go in rather than compressing the PDF afterwards — you keep more control and get a better result.
When exporting from Word, PowerPoint or Google Docs, look for a "minimum size" or "web quality" option in the export dialog. It downsamples images to screen resolution, which is usually all a recipient needs.
Scanning settings that avoid the problem
Most people scan at whatever the machine defaults to. A few changes make an enormous difference:
- Scan in greyscale, not colour, unless the colour carries meaning. Roughly a third of the size.
- 200 dpi is enough for reading. 300 dpi is for printing, 600 dpi is for archival work and is four times the file size of 300.
- Choose PDF, not TIFF, and let the scanner apply its own compression.
- Use black and white mode for plain text documents. It produces tiny files and is perfectly legible.
If it still will not fit
Do not keep compressing until the document is unreadable. Put the file in cloud storage and send a link instead — Google Drive, Dropbox and OneDrive all do this in two clicks, and the recipient gets the full-quality original.
For anything confidential, set the link to expire or require a password, and remember that a link in an email can be forwarded just as easily as an attachment.
Frequently asked questions
Why is my PDF so large?
Almost always because the pages are scanned images rather than text. Try selecting a sentence — if nothing highlights, every page is a photograph.
What is the maximum email attachment size?
Gmail and Outlook allow about 25 MB, but many company mail servers cut it to 10 MB. Under 10 MB is the safe target.
Does compressing a PDF lose quality?
Yes — pages are re-encoded as images, so text stops being selectable. On a scan you lose nothing meaningful; on a text document you do.