A scan small enough for e-mail or WhatsApp, still readable
Updated October 31, 2026
The scan is done, you attach it, and the mail client says the message is too large; or WhatsApp sends it and the other side opens a blurred photo with the numbers gone. A page photographed with a modern phone is a twelve-megapixel colour picture, and ten of them in a PDF weigh more than a mail server accepts. The scan does not need to be that big: a document page carries a few thousand letters, not a landscape.
This guide is about making the file small where it does not hurt, and about sending it so it arrives as a document rather than as a photo.
Why the file is big
Three things make a scan heavy: the number of pixels (a full camera picture has far more than a page needs), the JPEG quality (the camera saves at a quality meant for photos of people), and colour where there is none (a black-and-white contract stored as a colour picture). A scanner fixes all three: it saves the page at a document resolution, re-encodes it at a quality that keeps the letters, and stores plain-text pages as black and white.
Scan at the Small size
In Scan to PDF, set Size to Small (e-mail) before saving. Each page is rendered at about 200 dpi, enough for normal print, and then re-encoded in steps until it is small; the Balanced setting keeps 300 dpi for printing and archiving.
Use the Black & white filter on pages that are only text. A black-and-white page is stored as CCITT G4, a lossless fax encoding that is usually far smaller than a JPEG of the same page; that is the single biggest saving for a contract or a letter. Keep Natural for pages with a stamp, a signature in ink or a photo, and Grayscale for faded print; both stay JPEG.
Check it is still readable
Open the saved PDF on the phone and zoom in on the smallest print: the digits of an amount, a footnote, the serial number of an ID. If they are fuzzy, go back, set that page to Grayscale or Natural and save again at Balanced. Small is a trade; the size preset re-encodes until the file is small, and on a page with very fine print the readable version is the slightly larger one.
Send it as a document
In WhatsApp, attach the PDF through Document, not through the photo picker: a photo is re-compressed, a document is sent as it is. The same holds for Telegram and Messenger. In an e-mail, attach the PDF; if the mail client still refuses, run the file through Compress PDF with a target size, or split it with Split PDF and send the pages that matter.
On the receiving side, a PDF opens in any reader with the pages in order, which is also why one PDF beats ten photos in a chat.
What the tool does not do
It does not promise a size: the Small preset re-encodes each page until it is small, but a page full of colour photos stays larger than a page of text, and the honest check is the size shown after saving. It does not send the file for you; it saves it on the phone or hands it to the share sheet. It cannot make an illegible picture legible by compressing it less: a blurred page is blurred at any size, so retake it.
Tips
- Searchable text adds little to the file: the invisible text layer is small compared with the pictures.
- A long receipt scanned in the Receipt format and Black & white is one narrow page and weighs very little.
- Save as JPG per page (ZIP) when the recipient wants pictures rather than a PDF; the size preset applies to them too.
- Check the size the tool shows after saving before you attach the file.
- For a file that must fit under a stated limit, Compress PDF with a target in KB is the right tool after the scan.
Questions
- What size does e-mail accept?
- Most providers refuse attachments above 20 to 25 MB, and some corporate servers much less; the guide on attachment limits has the numbers per provider.
- Why does WhatsApp blur my scan?
- Because it was sent as a photo. Send the PDF as a document and it arrives unchanged.
- Is the scan uploaded to make it smaller?
- No. The size preset, the filters and the PDF are computed on your phone; nothing is sent anywhere.