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PDF fonts

Silktide checks how the fonts inside a PDF are built. An accessible PDF has to carry its fonts with it, describe them consistently, and never draw a character the font cannot actually produce, so that the text is reproduced identically everywhere and stays readable by software.

This covers several requirements at once: fonts that are not embedded, embedded fonts whose internal descriptions disagree with the font itself, encodings the standard does not permit, and text drawing a font's missing-character placeholder.

Why this matters

These requirements split into two groups, and it is worth being honest about the difference.

Missing fonts and missing characters change what a reader gets. A font that is not embedded is only available if the reader happens to have it installed. When they do not, the viewer substitutes something else, and substitution changes character widths, so lines rewrap, tables lose their alignment, and text can overflow a box and disappear underneath something else. The placeholder is a stronger version of the same problem: it means a character the font cannot draw is being shown as a hollow box or blank, so the text on the page is already wrong and there is no character behind it for a to announce.

The consistency rules are file bookkeeping. Requirements about character sets, width tables, and permitted encodings are internal agreements inside the file. A reader usually notices nothing, and text extraction can be unreliable at the edges. They matter because they are part of the standard, so they block a conformance claim, and because they are a reliable signal that the document came out of a workflow that was not paying attention to fonts.

Both groups are worth reporting, and they do not deserve the same urgency. Silktide grades them differently for exactly that reason.

How to fix it

  1. Re-export from the source with all fonts embedded. This is the fix for nearly every finding here, because the export process is what writes the font data and its descriptions. Most tools embed fonts by default now, so an old file usually just needs exporting again from a current version.
  2. Do not print to PDF. Print drivers are the most common cause of font damage, because they describe a page as marks rather than as text. Use the application's own export or "Save as PDF".
  3. Check that your fonts allow embedding. A licensing flag can forbid it, in which case the document will not embed them, however you export. Substituting a font you can embed is the practical answer.
  4. Fix missing characters at the source, usually by using a font that contains them. The placeholder appears when a document asks for a character its font does not have, which is common with unusual punctuation, accented characters, and mathematical symbols.
  5. Or run Silktide remediation, which embeds a faithful substitute where a free equivalent exists. There are limits to what substitution can do, and they are documented in Fonts.

Note that the consistency requirements cannot be repaired with a PDF editor's accessibility tools. They are properties of the embedded font data, so re-exporting is the route, and where that is impossible, partial conformance is a reasonable outcome to accept and record.

How Silktide tests this

  1. Find the PDF documents linked from your website, and analyse each unique file once, however many pages link to it.
  2. Examine every font the document uses: whether it is embedded, whether its declared character set and widths match the embedded font data, and whether its encoding is one the standard permits.
  3. Examine the text-drawing instructions for any that draw the font's missing-character placeholder.
  4. Report the document when any of those fail, once per document however many fonts are affected.

Text whose characters cannot be traced back to real characters is a related but separate finding, reported by PDF text mapping.

Troubleshooting

The document looks correct on my machine

That is the expected symptom of a font that is not embedded: you have the font installed, so your viewer uses it. Someone without it sees a substitute. This is why the check reads what the file carries rather than what it renders locally.

The finding mentions character sets or glyph widths and the text looks fine

It probably is fine to read. Those are the internal consistency rules described above: they block a formal conformance claim and rarely change what anyone sees. If you cannot re-export the document, this is a reasonable finding to rather than chase.

Only symbols and special characters are affected

That is the usual pattern, because documents mix a text font with an icon or symbol font and only the second is incomplete. Check bullets, tick marks, arrows, and mathematical characters.

Can Silktide fix the fonts without changing how the document looks?

Substitution aims to keep the page rendering identical, and where a metric-compatible free font exists it succeeds. Where none does, there is a visible trade-off, and the limits are set out in Fonts.

Learn more

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