Compress a scanned PDF
A scanner or a scanning app saves each page as an image, often at 300 DPI or more and with little compression. Ten pages can come to 20 MB, even though the same pages typed would be a few hundred kilobytes.
What compressing a scan does
Compress PDF goes through the PDF image by image. Each page image is saved again as a JPEG at a resolution that suits reading and printing, and placed back exactly where it was. The page size, the order of the pages and everything else in the file stay as they were. If the scan has a text layer (from OCR), it is not touched, so you can still search and copy text.
Which level to choose
- High quality keeps the most detail. Good for documents with fine print, stamps or signatures you want to look sharp. The file shrinks less.
- Balanced is the recommended level. For an ordinary 300 DPI scan of letters, forms or receipts, text stays clear and the file is usually around 90% smaller.
- Smallest file reduces most. Normal-size text stays readable, but very small print and photos can look softer. Use it when you have to meet a strict size limit.
If you are unsure, start with Balanced, open the result and zoom in on the smallest text on the page. If it looks fine, you’re done.
What it doesn’t change
Compress PDF doesn’t straighten pages, remove blank pages, change the scan to black and white or run text recognition. Those change what the document looks like; compressing only changes how efficiently the same pages are stored.
Some images are left as they are because recompressing them would change the document: images in print colors (CMYK), images with a wide-gamut color profile and a few rare kinds of transparency. The result tells you how many, in plain words.
Doing it in Compress PDF
- Open the scanned PDF. It stays on your device.
- Choose Balanced, or another level, and press Compress PDF.
- Check the size and the result; the new file ends in -compressed.pdf and your original is unchanged.