Your PDF is too big to e-mail. Here is what is actually in it
Most oversized PDFs are oversized for one reason: photographs. Learn to tell a scan from a text document, pick a sensible compression level, and get under the 25 MB limit without wrecking the file.
· 4 min read
Gmail stops at 25 MB. Outlook.com stops at 20 MB. Plenty of corporate mail servers stop at 10 MB. And the scan of a six page contract from your phone weighs 38 MB.
Before you compress anything, it helps to know what is taking up the space.
Text is tiny. Pictures are not
A PDF full of text is remarkably small. A hundred page book, text only, fits in a couple of megabytes, because the file stores letters and a reference to a font, not a picture of each page.
The moment a page becomes a photograph, that changes. A single phone photo of an A4 sheet is 3 to 8 MB. Six of them and you are past every mail limit, for a document that would have been 200 kB if it had been exported rather than photographed.
So there are really two kinds of large PDF:
| What it is | What helps | |
|---|---|---|
| Exported from Word, an invoicing app, a browser | Text plus a few images | Little to compress; it is already small |
| Scanned or photographed | Every page is one big picture | Compression, and a lot of it |
If your file came out of a scanner or a phone, compression will do a lot. If it came out of Word and is still huge, look for embedded images at print resolution, or fonts embedded in full rather than subset.
How compression actually works here
Compressing a PDF mostly means re-encoding the images inside it: lower the JPEG quality, and often lower the resolution too. The page layout, the text and the structure stay untouched.
The trade is straightforward. Fewer bits per photo means a smaller file and softer detail. For a scanned contract, softer detail is fine, because you only need the letters to be legible. For a portfolio of product shots, it is not.
Compress PDF gives you three levels, and the honest advice is to start in the middle:
- Light keeps close to the original and typically saves a quarter to a third. Use it when the document has photographs you care about.
- Balanced is the one to reach for by default. Scans usually drop by half or more and stay perfectly readable.
- Strong goes further, and text stays legible, but photographs start to show artefacts.
Check the result before you send it. Open the compressed file and look at the smallest text on the busiest page. If you can read that, you are fine.
When compression is the wrong answer
The file is huge because it has 400 pages. Compression will not fix that. Split it and send the part the other side actually needs.
Someone wants to look at one page. Export that page as an image with PDF to JPG and put it in the body of the mail. No attachment, no download, no confusion.
You scanned at 600 dpi. Documents do not need it. 300 dpi is archival quality for text, 200 dpi is fine for everyday use. Rescanning at a sane setting beats compressing a bloated file.
It is already a text PDF at 900 kB. There is nothing to squeeze. If your mail server is refusing that, the problem is the server, or the total of several attachments.
A note about scanning apps
Phone scanning apps often default to the highest quality they can produce, on the theory that you can always compress later. That is defensible, but it means the file you share is rarely the file you should share.
If your app has a quality setting, medium is the right default for documents. If it offers black and white or greyscale for text pages, use it. A greyscale scan of a printed page can be a tenth the size of the colour version and no harder to read.
Frequently asked questions
How much smaller will my PDF get?
For a scanned document, expect half or better at the balanced level. For a PDF exported from an office program, expect very little, because there was no wasted data to begin with.
Does compressing a PDF lose quality?
Yes, in the images. Text and layout are untouched, so the document stays selectable and searchable. At the balanced level the difference on a scan is hard to see.
Can I compress a file more than once?
You can, but it rarely helps and each pass costs quality. If one pass at balanced is not enough, use the strong level on the original rather than compressing the compressed file.
Is there a size limit?
Free accounts handle files up to 25 MB, Premium up to 200 MB. The work happens in your browser, so very large files also depend on your device having the memory for them.
Will the text still be searchable afterwards?
Yes. Compression touches the images, not the text layer. If your file was a plain scan with no text layer, it had nothing searchable in it before compression either; that needs OCR.