OCR (Optical character recognition or optical character reader) is needed for image PDFs (e.g. scanned data). This option uses more credits and therefore should only be activated for image PDFs.
This will not return images in the PDFs you upload, but will convert text in images to text for you to use in your Tools.
The error message similar to the one below indicates that a non-PDF file was uploaded to the Tool step. Only PDF files are supported.
Unsupported file type: xlsx