Thank you for testing that out for me, @Yoichi . Much appreciated.
EDIT: Such a simple solution, just having a string with .bmp at the end. I should have thought of that! Nice.
EDIT 2:
I tried this out myself today (2/23/24), and I actually did not see that error with a .bmp file (or .gif file, which I was also curious about).
I tried again with a completely different filetype I was sure would not be accepted (.HEIC), and it said “Digitize Document - Digitize: The extension ‘.HEIC’ does not have a known content type defined.”
I tried with .txt, and got the error message @Yoichi received earlier: “Digitize Document - Digitize: Unsupported content type: text/plain.” So I think with UiPath.IntelligentOCR.Activities 6.5.0, .bmp and .gif are accepted, even though this says they are not: Activities - Digitize Document (uipath.com)