Handling Defective PDF Files with Relaxed Syntax

Overview

This document provides insights into addressing minor syntax errors in PDF files, especially when dealing with defective files that generate exceptions during processing. It discusses the implications of relaxing syntax rules, common errors, and the limitations of current solutions.

Common Issues with Defective PDF Files

When handling defective PDFs, syntax errors often lead to exceptions during rendering or processing. Examples of such errors include:

• Bad Font Object or Font Descriptor:
• These errors occur due to corrupted font data in the PDF file.
• Viewer Variability:
• Different PDF viewers handle defective files differently:
• Chrome: Substitutes fonts dynamically and displays content.
• Safari/Mac Preview: Displays the PDF but omits text for certain pages.
• Acrobat: Displays error messages or omits content based on the corruption severity.

Relaxing Syntax Rules for Minor Errors

APDFL, allow the use of relaxed syntax settings to bypass certain minor syntax issues. This approach enables the processing of slightly defective files under specific circumstances.

Enabling Relaxed Syntax

To implement relaxed syntax handling in APDFL, the PDPrefSetAllowRelaxedSyntax API can be used. This option lets the system ignore a limited set of syntax issues or apply reasonable defaults:

#include "DLExtrasCalls.h"
PDPrefSetAllowRelaxedSyntax(true);

Use Cases and Limitations

• Use Cases:
• Resolves discrepancies where Acrobat processes a file but APDFL throws an exception.
• Allows certain operations to proceed without raising errors for minor issues.
• Limitations:
• This setting does not address severe issues like font corruption.
• Ignoring critical errors, such as bad font objects, can lead to unintended visual or functional discrepancies in the output.

Example Scenarios

Error Reproduction

The following methods and tests reproduce errors in defective PDF files:

• Using APDFL’s PDPageDrawContentsToMemoryWithParams method:
• Generates exceptions such as “Bad font object or font descriptor object.”
• Occurs with files containing corrupted font data.

Viewer Behavior

• Chrome substitutes fonts dynamically, ensuring content display despite the corruption.
• Safari and Mac Preview fail to render text from page 3 onward in severely defective files.
• Acrobat either omits text or displays error messages, depending on the corruption level.

Recommendations

• Diagnostic Questions:
• Are these one-off defective files or part of a larger dataset with similar errors?
• Can source files be regenerated with proper font embedding and structure?
• Relaxed Syntax Usage:
• Use PDPrefSetAllowRelaxedSyntax for minor issues only, ensuring that critical workflows are unaffected.

Conclusion

Relaxing syntax rules can be an effective workaround for minor PDF defects but should not be considered a solution for severe file corruption. Addressing font-related errors requires thorough diagnostics and file repair to ensure accurate rendering and functionality across all viewers. For further assistance or if defective files are part of a larger recurring issue, contact the support team for tailored solutions.