Add PDF source support to DeepSearch

## Summary DeepSearch currently does not support PDF indexing. To enable this, raw binary PDF files must be downloaded to a temporary location for interpretation and chunking. ## Steps to Reproduce Not provided. ## Expected Behaviour DeepSearch should support PDF sources by downloading raw binary to a temporary location, interpreting the content, and chunking it. ## Actual Behaviour DeepSearch does not support PDF indexing. ## Environment Not provided. --- *Reported by **retoor** via DevPlace.*