A phone camera records far more detail than a form needs. Every scanned page is stored as a photo, so a five-page scan can be many megabytes even though it only holds a little text.
Why scans compress well
Compression reduces the images inside the PDF: fewer pixels and stronger image compression. Scans are almost entirely images, so they have the most to gain. Text-only PDFs, by contrast, are often small already and change little.
How far a scan can go depends on:
- Pages. The limit is shared between all of them.
- Content. A page of plain text on white compresses much better than a colour photo or a page with shading.
- Scan quality. Shadows, a tilted page and grainy low-light photos leave “noise” that is expensive to store.
Compress an existing scan
- Open PDFTuck and tap Select PDF.
- Choose the limit you need, from 200 KB to 10 MB, or a Custom value. If there is no strict limit, choose Balanced instead.
- Tap Compress PDF and wait for the result. You can cancel at any time.
- In Preview, zoom in on the smallest text. If it is too soft, try a slightly larger limit if the form allows it.
- Save or share the new file. The original scan stays exactly as it was.
Scan smaller next time
- Lay the page flat, in even light, without your shadow on it.
- Use your scanner app’s document mode, which crops and straightens the page.
- If colour doesn’t matter, choose black and white or greyscale.
- Scan only the pages the form asks for.
Each of these makes the file smaller before compression even starts, and the compressed result sharper.
When very small limits meet many pages
Divide the limit by the number of pages to see how much room each page gets. Ten pages under 200 KB is 20 KB a page, which is very little for a photo. If PDFTuck reports Best readable result instead of Ready to upload ✓, split the scan into parts or remove pages, rather than forcing a file nobody can read.