You open a contract and the headings look like a typewriter from 1974. Or someone sends a CV where every other word is in a different typeface. The PDF isn't broken — it's just guessing.
The viewer is doing its best
When a font isn't embedded in the PDF and isn't installed on your computer, your viewer picks the closest match. That's why everything sometimes turns into Courier or Times. The file knows it wanted Helvetica Neue Light; your computer offers whatever's closest. The original document on the sender's machine looked fine; on yours it's been auto-translated. Opening it in Flint lets you replace text with fonts that exist everywhere.
Old PDFs and Asian characters
Older or scanned PDFs sometimes use legacy encodings that modern viewers stumble over. Chinese, Japanese and Korean text especially can show as boxes or question marks if the right CJK font pack isn't installed. The text is fine in the file — it's a display issue. Updating your PDF viewer usually fixes it. For documents you'll keep, re-saving from Flint with embedded fonts makes them future-proof.
When fonts look ransom-note mixed
If part of the text looks normal and part is weird, the PDF embedded *some* fonts but not all of them. Common culprits: pasted text from another source, edits made in a viewer that doesn't re-embed. You can patch this by retyping the odd lines using a standard font in /edit-pdf, then saving a fresh copy.
FAQ
Can I install the missing font?
Usually yes — Google Fonts and Adobe Fonts cover most common typefaces for free. Install the font, restart your viewer, and the PDF should render correctly. Worth it for documents you reference often.
Why do some PDFs use Courier when it shouldn't?
Courier is the universal fallback most PDF viewers reach for when they have no other option. If you see Courier, the file is almost certainly missing an embedded font.
Will printing fix the fonts?
Sometimes — printers have their own font fallback chain. But what comes out is usually whatever your screen showed, weird fonts and all. Fix it in the file first.
Weird fonts are almost always missing fonts. Open the PDF in Flint, retype the offending bits, and save — your future self will thank you.