Why Your PDF File Is Too Large, and How to Fix It
Guide · PDF Tools
A PDF that's much larger than it looks like it should be is almost always down to one specific culprit: uncompressed or oversized embedded images. Text and vector graphics take up very little space in a PDF; high-resolution photos, especially several of them in one document, are what actually drive file size up.
Scanned documents are the worst offenders
A scanned page is really just a photo of a piece of paper, and if it's scanned at high resolution and saved without compression, a ten-page scanned document can easily be many times larger than a ten-page document created digitally with real text. Scanner software often defaults to higher resolution than the content actually needs — a plain text document rarely needs to be scanned at photo-quality settings.
What compression actually does to a PDF
A PDF compressor typically re-compresses the embedded images at a lower quality setting and may also strip unnecessary embedded data (unused fonts, duplicate resources), shrinking the overall file without altering the visible text content at all — text stays crisp because it's not stored as an image in the first place.
How much compression is safe for a scanned document
For a scanned document where readability is the priority, moderate compression usually keeps text perfectly legible while meaningfully reducing file size — the point where compression starts to hurt is when it's pushed so far that the scanned page's fine details start to blur, which is a visible, checkable threshold rather than a guessing game.
When to compress vs when to fix the source
If a scanned document consistently comes out oversized, check the scanner's resolution setting — dropping from a very high DPI setting to something more reasonable for text (150-200 DPI is usually plenty) fixes the problem at the source, rather than compressing an unnecessarily large file after the fact every time.