Method getFileId

src/parser/document-parser.ts:883–897

* Extract the file ID from the trailer's /ID array. * Returns the first element of the array (the permanent file ID).

(trailer: PdfDict)

   * Returns the first element of the array (the permanent file ID).
   */
  private getFileId(trailer: PdfDict): Uint8Array | null {
    const idArray = trailer.getArray("ID");

    if (!idArray || idArray.length < 1) {
      return null;
    }

    const firstId = idArray.at(0);

    if (firstId instanceof PdfString) {
      return firstId.bytes;
    }

    return null;
  }

  /**
   * Check if bytes at position match a pattern.