How to compress a PDF for WhatsApp on Android
A scan of six pages can easily run to 15 MB, and that is fine for WhatsApp itself. It stops being fine when the person receiving it has to upload the file to a portal that refuses anything over 200 KB, or forward it to an inbox that bounces large attachments.
This guide covers what WhatsApp does and does not do to a document you attach, what actually makes a scanned PDF smaller, and the exact steps to compress one in ScanCrypt without the file leaving your phone.
What WhatsApp does with a document you attach
WhatsApp’s help page for Android lists Document alongside Camera, Gallery and Audio, and describes it as a file "of up to 2 GB from your phone" (WhatsApp Help Center, read 2 September 2026). A scanned PDF is nowhere near that ceiling, so a document that will not go through is almost never hitting WhatsApp’s limit.
The same page describes no size-reduction step for documents. Photos and videos have their own entries in that list because they are handled as media; a document is the file you picked. That is why the pressure to compress rarely comes from WhatsApp itself.
- A government or university portal that caps an upload at 100 KB, 200 KB or 1 MB.
- An email gateway on the other end that rejects the attachment once it is forwarded.
- A slow or metered connection, where a 15 MB send stalls and the recipient gives up.
- A recipient on a nearly full phone who cannot download the file at all.
What actually shrinks a scanned PDF
Zipping a PDF does close to nothing. The bulk of a scan is page images that are already JPEG-compressed, and a general-purpose archiver cannot squeeze data that is already compressed. The only real lever is to re-encode those page images at a lower JPEG quality and, usually, at a smaller pixel size.
That is the trade ScanCrypt puts in front of you. If your PDF has a real text layer, the Compress screen offers to keep it, which means a lossless re-save that preserves selectable and searchable text and shrinks almost nothing. Turn that off and the pages become images: much smaller, but the text can no longer be selected or searched.
Once you accept the image route, the three quality presets differ in JPEG quality and in how far the page is scaled down.
- Low (smallest) — about 40% JPEG at 60% of the page scale. The heaviest reduction.
- Medium — about 65% JPEG at 80% scale. The default, and the balanced choice.
- High (best quality) — about 85% JPEG at the original scale. A modest saving.
Hitting a 100 KB, 200 KB or 1 MB limit
ScanCrypt has no "target size in KB" box. You pick a quality and the screen shows the current size next to an estimated output size and a rough percentage saved, so you can judge before committing. Start at Medium, read the estimate, and drop to Low if it is still above the cap.
If Low is not enough, the file itself is the problem rather than the setting. A 100 KB cap on a form usually assumes a single page, so split the document and send only the page that is asked for. Failing that, export the pages as JPEG images and compress those individually — both of those tools are free — and attach the image the form actually wants.
- Check the estimate before you compress, not after.
- Fewer pages beats a harsher quality setting for readability.
- Export as JPG plus Compress Image is the route when a form wants a picture, not a PDF.
How to do it in ScanCrypt
- Scan or import the PDF first. Compress works on a document in your ScanCrypt library, so the file needs to be there before you start.
- Open Tools and tap Compress. Then pick the PDF from the list. The screen opens on your file and reads its current size.
- Decide about searchable text. If the PDF has a text layer, a "Keep searchable text" switch appears. Leaving it on preserves selectable text but barely changes the size. Turning it off lets the pages become images, which is where the real reduction comes from.
- Choose a quality. Low (smallest), Medium or High (best quality). Each row shows the estimated output size and roughly how much you save.
- Tap COMPRESS. The result is written as a new file ending in _compressed.pdf. Your original is left exactly as it was.
- Send it to WhatsApp. Share the compressed file to WhatsApp like any other file. From the document viewer there is also a COMPRESS & SEND action that compresses at the Medium preset and hands the result straight to WhatsApp in one tap.
Questions
Will compressing make the text unreadable?
At Medium, printed text on a normal scan stays clearly legible — that preset keeps 80% of the page scale. Low drops to 60% scale and about 40% JPEG quality, which is where small print and thin handwriting start to smear. Check the estimate, try Medium first, and keep the original in case you need to redo it.
Is Compress free?
Yes. Compress is available on the free tier, with ads. A Pro purchase removes the ads but does not unlock the tool, because it is not locked.
Does compressing replace my original PDF?
No. The compressed copy is saved as a separate file with _compressed added to the name, in the same ScanCrypt documents folder. Nothing overwrites the original.
Does it work without an internet connection?
Yes. The pages are re-encoded on the device, so compression works in airplane mode and the file is never uploaded anywhere.