AxCrypt can encrypt most of the file types. Also some file types AxCrypt will not encrypt due to security reasons.
AxCrypt will not encrypt any system files and operating system installed Files/Folders. So please avoid securing that kind of folders.
Because AxCrypt encrypted files will have a special file extension .axx and those will be opened only with the AxCrypt app.
If the above does not help,please provide more information about the issue and write a mail to firstname.lastname@example.org . you can send a screenshot showing where the problem is, it often helps us understand.