How to Use the Command 'pdf-parser' (with Examples)

PDF files are ubiquitous in data exchange, whether for eBooks, legal documents, or brochures. While typically viewed for their content, sometimes it’s necessary to dive deeper into the structure of a PDF for analysis, troubleshooting, or security purposes. The command-line utility pdf-parser serves this need by allowing users to inspect the fundamental elements of a PDF without rendering it. This lightweight tool, created by Didier Stevens, provides powerful insights by parsing PDFs to reveal structural and metadata details.

Use Case 1: Display Statistics for a PDF File

Code:

pdf-parser --stats path/to/file.pdf

Motivation:

Understanding the overall structure of a PDF file can be invaluable, especially when assessing the document’s integrity or exploring potential vulnerabilities. Displaying statistics of a PDF file can provide a quick overview of its contents, including the number of objects, streams, and cross-reference tables, which are critical for verifying the file’s authenticity and consistency.

Explanation:

• pdf-parser: The command-line tool used to parse PDF files.
• --stats: This argument specifies that the user wants to display statistics related to the PDF file. It triggers the tool to outline a summary of the core components, providing a macroscopic view of the file’s structure.
• path/to/file.pdf: This represents the path to the PDF file being analyzed. It informs the tool where to locate the file to execute the parsing process.

Example Output:

PDF Header: %PDF-1.7
%PDF-1.7 Objects: 123
%PDF-1.7 Streams: 50
%PDF-1.7 Comments: 2
%PDF-1.7 Xref Tables: 1
%PDF-1.7 Trailer: 1

This output indicates that the PDF uses version 1.7 of the PDF specification. It contains a total of 123 objects and has 50 streams. This information can help in comparing with expected values, particularly when verifying the integrity of the document.

Use Case 2: Display Objects of Type /Font in a PDF File

Code:

pdf-parser --type=/Font path/to/file.pdf

Motivation:

When dissecting a PDF for font-related issues, or examining document design from a technical standpoint, it is crucial to extract and inspect all font objects embedded within the document. This is especially important for preserving document fidelity when fonts are custom or not universally available.

Explanation:

• pdf-parser: The command-line tool used for parsing PDF files.
• --type=/Font: This argument focuses the parsing process on objects of type /Font. PDF files can contain various object types, and extracting fonts might reveal embedded font files or provide insights on how text is rendered.
• path/to/file.pdf: The file path to the PDF that needs analysis, indicating where the tool should perform its search.

Example Output:

obj 15 0
 Type: /Font
 Referencing: 10 0
 <<
 /BaseFont /Helvetica
 /FontDescriptor 14 0 R
 /Type /Font
 >>

obj 23 0
 Type: /Font
 Referencing: 10 0
 <<
 /BaseFont /Times-Roman
 /FontDescriptor 20 0 R
 /Type /Font
 >>

This output shows two font objects embedded within the PDF. Each displays its base font name, allowing users to verify or replace fonts if necessary for consistent display across different platforms.

Use Case 3: Search for Strings in Indirect Objects

Code:

pdf-parser --search=search_string path/to/file.pdf

Motivation:

Searching for specific strings within a PDF’s indirect objects can be vital for identifying sensitive data, hidden scripts, or any occurrences of particular elements within the document. It aids security professionals and developers in isolating potential risks or uncovering hidden content.

Explanation:

• pdf-parser: The command-line tool employed for parsing PDF files.
• --search=search_string: This argument conducts a search for a specified string within the PDF’s indirect objects. The search is exhaustive through the document’s metadata and hidden elements, rather than the visible text layer.
• path/to/file.pdf: Represents the PDF path intended for analysis, guiding the tool to locate and process the specified file.

Example Output:

obj 5 0
 Type: /Page
 Contains: search_string

obj 46 0
 Type: /EmbeddedFile
 Contains: search_string

The output provides details of each indirect object containing the search string. It indicates the specific object numbers and their types, helping trace where and how certain data or keywords are being used within the document.

Conclusion

The pdf-parser tool provides a strategic advantage when dealing with PDFs by dissecting the innards of a document rather than simply viewing surface content. Whether you’re assessing integrity, identifying embedded resources like fonts, or hunting for data strings, pdf-parser delivers a command-line solution that bypasses the need for conventional GUI-based PDF readers. This utility elevates your ability to perform deep analyses and reinforces PDF security by giving a clearer insight into a document’s structure and embedded content.