PDF is been seen differently by different users

Hello,

at my workplace we're having the issue right now, that for certain users, certain Files are shown in CT  and for other users the same file is a PDF file.

I've never seen that happening, especially with specific files, not as a general issue.

For clearance an example

Christa sees File 1 and File 2 as PDF

Elona sees them as File 1 (PDF) and File 2 (CT File)

Since CT files are also a file format provided by Adobe, I thought I might find help here.

Thanks in advance for your help.

Jonas