Why Is My PDF Blurry? (And How to Fix It)

The first thing to establish is whether the blur is in the file or in how you are looking at it. That takes one test.

The diagnostic

Try to select a line of text with your cursor.

Real text in a PDF is stored as outlines and renders sharply at any zoom. If it does not, the problem is your viewer, not the file.

The four causes

A low-resolution scan

Scanned below 200 DPI, the characters were captured blurry. Nothing recovers detail that was never captured — the only fix is rescanning at 300 DPI.

Over-compression

Aggressive compression downsamples images and re-encodes them heavily. If you still have the original, compress it again at a lighter setting. If not, the damage is permanent.

Rasterised text

Some tools convert pages to images during merging, converting or "flattening". Text that was crisp becomes pixels. Redo the operation with a tool that preserves text.

Viewer rendering

Some readers render at a fixed resolution and scale the result, which looks soft at certain zoom levels. Zoom to exactly 100%, or open the file in a different reader — if it is sharp there, the file was always fine.

Blurry when printed

• The source images are below 300 DPI — the usual cause.
• The print dialogue is scaling the page, softening everything.
• Draft or economy print mode is on.
• "Print as image" is enabled in the advanced settings, which rasterises everything.

Preventing it

Scan at 300 DPI. Compress once, at the end. Use tools that keep text as text. Keep the original of anything you compress — that single habit turns most of these problems from permanent into inconvenient.