How to reduce a scanned PDF's file size
By PDFEditor.ae · Published
Why scans are large
Every page of a scan is a picture. Colour, high resolution and wide empty borders all add to its size. Compressing afterwards helps little: our lossless Compress PDF does not touch images, and in our test a photo-based PDF did not shrink at all. The real savings come at capture time.
Settings that make the biggest difference
- Resolution: 200–300 DPI is usually enough for documents; higher settings mostly add size.
- Colour: use greyscale for black-and-white documents, but keep colour if stamps, signatures or highlights are coloured.
- Framing: crop away the desk or scanner bed around the page, without cutting off margin notes.
- Pages: skip blank backs when scanning double-sided documents.
Steps
- Look at one sample page and decide what detail must stay readable.
- Rescan or re-photograph with the settings above, or resize and crop the existing images.
- Turn the images into a PDF with JPG to PDF.
- Compare faint text, seals and handwriting with the original before replacing it.
A mistake to avoid
Converting everything to pure black and white can make faint handwriting disappear and turns coloured stamps into blotches. Only drop colour when it carries no information.
Does OCR make a scan smaller?
No. OCR adds a text layer so the scan can be searched; it usually makes the file slightly larger. Size and searchability are separate problems.