Opening a PDF and seeing question marks, boxes, or random symbols where text should be is a font rendering failure. The characters are there in the file โ the viewer just can't display them correctly. Understanding the specific cause points directly to the fix.
The Most Common Cause: Missing Font Embedding
When a PDF references a font that isn't embedded in the file and isn't installed on your device, the viewer can't render those characters. Rather than displaying nothing or crashing, most viewers show a placeholder โ a question mark, a box, or a bullet โ in place of each unrecognizable character. This is the viewer saying: "I know there's supposed to be text here, but I don't have the font needed to show it."
The fix depends on who created the PDF. If it's your own document, re-export with font embedding enabled โ in Word, go to File โ Options โ Save โ check "Embed fonts in the file." If you received the PDF from someone else, ask them to re-export with embedded fonts, or install the specific font on your system if you know which one it is.
Encoding Mismatch: Characters Outside the Font's Scope
A more technical cause: the PDF uses a font that's installed on your device, but the character encoding in the file doesn't match what the font expects. This happens most often with older PDFs, documents created in non-English languages with specific encoding requirements, or files exported from certain legacy software.
You'll usually see this with special characters โ accented letters, currency symbols, mathematical notation, or non-Latin scripts โ while basic Latin text renders correctly. The font is present but doesn't contain the specific characters being requested, or the encoding table that maps character codes to glyphs is broken.
Symbol Fonts and Dingbats
Some PDFs use symbol fonts โ Wingdings, Webdings, Symbol, Zapf Dingbats โ for decorative elements, checkboxes, or icons. These fonts map standard keyboard characters to symbols rather than letters. If the symbol font isn't embedded and isn't installed on your device, the characters display as question marks or boxes even though from the file's perspective they're ordinary text characters.
The clue is that the affected characters appear in patterns โ all the symbols in a list, all the decorative elements โ while body text renders normally. Opening the document properties and checking the font list confirms whether a symbol font is referenced without being embedded.
The Viewer Is the Problem
Occasionally the file is fine but the viewer is failing to render it correctly. Browser-based viewers sometimes struggle with PDFs that use advanced font features โ ligatures, OpenType layout features, or complex glyph substitution rules. A document that shows question marks in Chrome's built-in viewer may render perfectly in Adobe Reader or Preview.
Test by opening the same file in two or three different viewers. If it renders correctly in one and not others, the file is fine and the problematic viewer has a rendering limitation. Use the viewer that works, or download and open locally rather than relying on the browser viewer.
Fixing a PDF With Broken Character Rendering
If the file itself has the problem and you need to produce a clean, renderable version, running it through a PDF Editor or optimization tool can sometimes resolve encoding issues by rebuilding the font tables. For documents where the visual appearance matters more than the underlying text structure, printing to PDF (using a virtual PDF printer) flattens everything into a rasterized or re-encoded form that renders consistently regardless of font availability.
For the cleanest fix, go back to the source document, ensure the fonts are properly embedded, and re-export. This is the only approach that preserves the text layer and produces a file that will render correctly on any device without requiring specific fonts to be installed.