mozilla/pdf.js · error · FormatError

parseFDSelect: Unknown format "${format}".

Error message

parseFDSelect: Unknown format "${format}".

What it means

Thrown by CFFParser.parseFDSelect when the FDSelect table (CIDFont-only) has a format byte that is neither 0 nor 3 (the only defined formats). The default branch fires, indicating a corrupt FDSelect table.

Source

Thrown at src/core/cff_parser.js:1097

          let first = (bytes[pos++] << 8) | bytes[pos++];
          if (i === 0 && first !== 0) {
            warn(
              "parseFDSelect: The first range must have a first GID of 0" +
                " -- trying to recover."
            );
            first = 0;
          }
          const fdIndex = bytes[pos++];
          const next = (bytes[pos] << 8) | bytes[pos + 1];
          for (let j = first; j < next; ++j) {
            fdSelect.push(fdIndex);
          }
        }
        // Advance past the sentinel(next).
        pos += 2;
        break;
      default:
        throw new FormatError(`parseFDSelect: Unknown format "${format}".`);
    }
    if (fdSelect.length !== length) {
      throw new FormatError("parseFDSelect: Invalid font data.");
    }

    return new CFFFDSelect(format, fdSelect);
  }
}

// Compact Font Format
class CFF {
  header = null;

  names = [];

  topDict = null;

  strings = new CFFStrings();

View on GitHub (pinned to 5903d58d58)

Solutions

1. Let pdf.js fall back to a system font (it catches this FormatError).
2. Repair or re-embed the CIDFont using fontTools (ttx) or Ghostscript.
3. Re-subset the font with a compliant tool if produced in-house.

Example fix

// pdf.js substitutes a fallback font; observe via render promise.
try {
  await page.render({ canvasContext, viewport }).promise;
} catch (e) {
  console.warn('Render failed due to corrupt FDSelect format:', e);
}

null

null

try {
  await page.render({ canvasContext, viewport }).promise;
} catch (e) {
  // Corrupt CIDFont FDSelect format; pdf.js falls back to a system font.
  console.warn('Unknown FDSelect format:', e);
}

When it happens

Trigger: Parsing a CID-keyed CFF font whose FDSelect table begins with a format byte outside {0,3}. FDSelect maps each glyph to a Font DICT index and only formats 0 (per-glyph bytes) and 3 (ranges) are defined.

Common situations: Corrupt CIDFont FDSelect tables in embedded CFF2/CFF fonts; damaged font streams; output from subsetting tools that wrote an invalid FDSelect format; CFF2 fonts misrouted through the legacy CFF parser.

Related errors

• parseFDSelect: Invalid font data.
• Invalid CFF header
• CFF Private DICT extends past end of font
• Unknown charset format
• Unknown encoding format: ${format} in CFF

AI-assisted analysis of mozilla/pdf.js@5903d58d58 (2026-08-13). Data as JSON: /api/errors/42e2cdebfb76d632. Report an issue: GitHub.