A file named "image.pdf" is treated as an image

When I try to open a PDF file from an email with an attachment with a file name of “image.pdf”, it seems to be recognized as an image file and there is no PDF viewing app in the list of apps to open and I cannot open it. (PDF files with other names are still open.)

Because the attached PDF file is a normal PDF file, I save it and open it from another application to cope with it, but it would be helpful if it can be opened from K-9 Mail immediately.

Thank you.