Identify real file type

is there a way to detect the true file type of a file.
Possibly in the header of the file or in a similar way.
I have the problem that there are files on my hard drive that claim to be .pptx files. In reality, however, they are other files that only have the file extension .ppt or .pptx.
For example:, which is actually a .zip file.

Thanks in advance


the “file” command ?


I totally forgot about this command.

cheers F.K.