Why Is My PDF So Large? Causes and Fixes
The usual reasons a PDF is megabytes in size, how to diagnose them, and how to fix each one.
If a short document produces a PDF of 30 MB, one of a handful of causes is usually responsible.
High-resolution images
Phone photos and scans are the main culprit. A single 12-megapixel photo can be several megabytes. Fix by downsampling with Compress PDF Strong mode, or resize images before you build the PDF.
Scanning at too high a resolution
300 dpi colour scans of text pages are bigger than they need to be. 150 dpi is generally enough for reading, and black-and-white scanning is smaller still.
Embedded fonts
Fonts are embedded so the document looks the same everywhere. Many fonts embedded in full add up, though this is rarely more than a few hundred kilobytes.
Pages with large vector artwork
Maps, CAD drawings and complex diagrams can be heavy even without photos. Exporting a simpler version from the source program helps.
Leftover data
Some PDFs keep undo history, thumbnails or duplicate resources, particularly after repeated edits. A light compression pass re-saves the file cleanly.
How to check
Divide the file size by page count. Under 100 KB per page suggests mostly text. Over 1 MB per page means images. Test by converting one page to an image with PDF to JPG to see how heavy a single page is as a picture.