Fix #5930: Extract text from PDFs in ReadFileTool instead of returning base64

[devin-ai-integration]

Summary

Fixes #5930 — When using input_files with PDFFile, the read_file tool was base64-encoding the entire raw PDF binary and injecting it into the LLM context. This caused massive context bloat, inconsistent responses, and context overflow for even medium-sized documents.

Root cause: ReadFileTool._run() checked if the content type was a text type, and for anything else (including application/pdf) it fell through to a base64 encoding path.

Fix: Added PDF-specific handling in ReadFileTool._run() that uses pypdf (already a dependency via crewai-files) to extract structured text from PDF pages. Each page is labeled with a --- Page N --- header. Graceful fallbacks are provided for:

• pypdf not installed → short install instruction message
• No extractable text (image-only PDFs) → friendly diagnostic message
• Corrupted PDFs → error message (never base64)

The extracted text is dramatically smaller than base64-encoded binary, keeping the LLM context manageable.

Review & Testing Checklist for Human

• Verify that ReadFileTool._run() correctly extracts text from a real multi-page PDF (not just the synthetic test PDFs)
• Test with an image-only PDF to confirm the "no extractable text" fallback message appears
• Confirm that non-PDF binary files (images, audio, video) still return base64 as before
• Run a full crew kickoff with input_files={"doc": PDFFile(source="path/to/real.pdf")} and verify the agent receives readable text, not base64

Notes

• pypdf is already a dependency of crewai-files, so no new dependencies are introduced
• The fix only affects the read_file tool path — files that are auto-injected via multimodal LLM support (e.g., images on GPT-4o) are unaffected
• Added 6 new test cases covering: single-page extraction, multi-page extraction, blank PDFs, corrupted PDFs, missing pypdf, and size comparison vs base64

Link to Devin session: https://app.devin.ai/sessions/0922c01f2b064a7e8e0a6a2f05e9ab09

[devin-ai-integration]

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