Possible reasons (in random order):
- Because file conversion tools aren't available on the command line. For a list of required converters, see
- Because the file transform isn't registered in Portal Transforms. To add a pdf to text converter: Go to portal_transforms, click 'Add' (Transform), give it an id of 'pdf_to_text' and Module 'Products.PortalTransforms.transforms.pdf_to_text'. This step may be required when converters weren't available on the system during the Zope installation.
- Because the "File" type was disabled in @@search-controlpanel