How to test PDF compression quality

Updated 25 September 2026

A smaller PDF is only useful if it still does its job. Five minutes of checking avoids sending an unreadable contract or a blurry portfolio.

1. Know your target

Write down the actual limit: 10 MB for an email, 2 MB for an upload form, "as small as possible" for an archive. Then try levels from gentle to strong and stop at the first one that fits.

2. Compare the numbers

Compress PDF shows the exact size before and after for each level. If a level can't make the file smaller, it tells you and keeps the original — don't keep trying the same level. Documents that are mostly text often only shrink with the lossless level; scans and photo-heavy files shrink most with Balanced or Strong.

3. Check what matters

Small print — zoom to 200% on the page with the smallest text (footnotes, tables, signatures).
Photos and charts — look for blockiness in smooth areas and blur on fine lines.
Selectable text — try selecting and searching a word. The "Pages as images" level turns pages into pictures, so this stops working.
Links and forms — click a link, type into a form field. Balanced and Strong keep both; "Pages as images" does not.
Print — if it will be printed, print one test page; screens hide what paper shows.

4. Compare side by side

For a precise check of a critical page, convert that page from both files with PDF to JPG at the same DPI and look at them next to each other. To confirm no text changed, copy the text from both versions into the diff checker.

5. Keep the original

Compression is one-way. Keep the original file and send the compressed copy.