mozilla/pdf.js · warning · FormatError

Encoding is not a Name nor a Dict

Error message

Encoding is not a Name nor a Dict

What it means

Thrown when a font's /Encoding entry is neither a Name (e.g. /WinAnsiEncoding) nor a Dictionary (containing /BaseEncoding and /Differences). Per the PDF spec, /Encoding must be one of those two forms. Unlike most guards here, this one is gated by options.ignoreErrors — if stopAtErrors is false it degrades to a warning and falls back to a default encoding.

Source

Thrown at src/core/evaluator.js:3677

            const data = xref.fetchIfRef(entry);
            if (typeof data === "number") {
              index = data;
            } else if (data instanceof Name) {
              differences[index++] = data.name;
            } else {
              throw new FormatError(
                `Invalid entry in 'Differences' array: ${data}`
              );
            }
          }
        }
      } else if (encoding instanceof Name) {
        baseEncodingName = encoding.name;
      } else {
        const msg = "Encoding is not a Name nor a Dict";

        if (!this.options.ignoreErrors) {
          throw new FormatError(msg);
        }
        warn(msg);
      }
      // According to table 114 if the encoding is a named encoding it must be
      // one of these predefined encodings.
      if (
        baseEncodingName !== "MacRomanEncoding" &&
        baseEncodingName !== "MacExpertEncoding" &&
        baseEncodingName !== "WinAnsiEncoding"
      ) {
        baseEncodingName = null;
      }
    }

    const nonEmbeddedFont = !properties.file || properties.isInternalFont,
      isSymbolsFontName = getSymbolsFonts()[properties.name];
    // Ignore an incorrectly specified named encoding for non-embedded
    // symbol fonts (fixes issue16464.pdf).

View on GitHub (pinned to 5903d58d58)

Solutions

1. Set stopAtErrors: false (or omit it) so this specific check degrades to a warn() and uses a fallback encoding, allowing the rest of the document to render.
2. Repair the PDF with qpdf or Ghostscript to rebuild the Encoding entry.
3. If authoring, ensure each font /Encoding is either a predefined Name or a proper encoding Dictionary.
4. Filter such PDFs upstream if text fidelity is required, since fallback encodings will mis-map glyphs.

Example fix

// before
getDocument({ url, stopAtErrors: true }); // throws on bad Encoding

// after
getDocument({ url }); // ignoreErrors defaults true -> warn + fallback encoding

// This guard is already gated by options.ignoreErrors in PDF.js itself.
// To benefit from the degrade-to-warning path, do NOT set stopAtErrors:
const pdf = await getDocument({ url /*, stopAtErrors: false is default */ }).promise;
// The font will load with a fallback encoding; only a console.warn is emitted.

When it happens

Trigger: A font dictionary whose /Encoding is a string, number, array, null, or any non-Name non-Dict object. Fires in PartialEvaluator.translateFont during page/font load. With ignoreErrors=true (the default render path) it logs a warning and continues; with stopAtErrors=true it propagates as an exception.

Common situations: Corrupt or non-conformant PDFs from buggy generators. Also appears after partial PDF repair tools that stripped the encoding object. Frequently seen alongside other font errors in scraped/faxed documents.

Related errors

• Invalid entry in 'Differences' array: ${data}
• FontFile should be a stream
• FontFile is empty
• Max size of CID is 65,535
• invalid font Subtype

AI-assisted analysis of mozilla/pdf.js@5903d58d58 (2026-08-13). Data as JSON: /api/errors/5f1ab2233ff57c77. Report an issue: GitHub.