I'm building a compliance tool that has to process PDFs securely

Here’s a practical security checklist for processing PDFs in a compliance tool:

1) Treat PDFs as untrusted input

• Assume PDFs can be malformed or malicious.
• Parse with a hardened, maintained library.
• Never trust embedded metadata, filenames, or extracted text.

2) Isolate PDF processing

• Run parsing/conversion in a sandboxed worker, container, or VM.
• Use least privilege: no network, read-only filesystem, minimal OS capabilities.
• Set CPU, memory, and wall-clock time limits to prevent DoS via zip-bomb-like PDFs or huge objects.

3) Disable active content and risky features

• Block JavaScript, launch actions, external links, embedded files, forms if not needed.
• Prevent auto-loading remote resources.
• Strip attachments and annotations unless explicitly required.

4) Protect against common PDF attacks

• Validate structure and file size before deep parsing.
• Defend against:
  • Recursive object graphs
  • Oversized streams
  • Image bombs
  • Font parsing bugs
  • Incremental update trickery
  • Encryption/password edge cases
• Keep libraries patched; PDF parsers often have CVEs.

5) Secure rendering and OCR pipelines

• If converting PDFs to images or text:
  • Use a separate isolated service.
  • Limit DPI and page dimensions.
  • Sanitize image inputs after rendering too.
• For OCR, assume the OCR engine is also untrusted if it processes user-controlled files.

6) Handle sensitive data carefully

• Encrypt documents at rest and in transit.
• Control access with strong authn/authz and audit logging.
• Avoid logging raw PDF contents or extracted PII.
• Redact sensitive fields in outputs and debug logs.

7) Validate outputs

• Extracted text and metadata should be normalized and escaped before use in HTML, SQL, JSON, or shell commands.
• Treat filenames and metadata as hostile to prevent injection/XSS/path traversal.

8) Build operational safeguards

• Rate limit uploads and processing.
• Virus/malware scan files if appropriate, but don’t rely on scanning alone.
• Monitor for crashes, hangs, memory spikes, and repeated parse failures.
• Keep a quarantine path for suspicious documents.

9) Prefer safer architectures

• If possible, use:
  • A stateless document processing microservice
  • Queued asynchronous processing
  • Ephemeral workers that are destroyed after use
• Never process PDFs in the main web app process.

10) Test offensively

• Add a corpus of malicious PDFs and fuzz your parser.
• Include regression tests for known CVEs and edge cases.
• Verify sandbox escape resistance and timeout behavior.

If you want, I can turn this into:

1. a secure reference architecture,
2. a threat model for PDF ingestion, or
3. a concrete implementation checklist for your stack (e.g., Python/Java/.NET/Node).