1. Define accepted files. Limit types, sizes and counts according to the task. Validate content beyond filename extensions. Do not process every format because a library can open it; reduce the surface to what the product needs.
2. Isolate processing. Conversion, OCR and extraction need time, memory, filesystem and network limits. Keep libraries updated. A policy applied to final text cannot prevent exploitation of a vulnerable parser at an earlier stage.
3. Process extracted content. Documents and images may contain names, identifiers and hostile instructions. Apply the organization's policy before inference and treat source text as data. Assess protection of original files separately.
4. Verify predictable failures. Test corrupted files, large images, pages without text and documents carrying hostile instructions. The system should report failures, constrain resources and allow recovery. Review temporary files and retention after both successful and failed processing.