Formerly I copied a ttf-file to C:\\Windows\\Fonts, clicked the file to display the font, then clicked on [Install] and everything was fine.
When I do this procedure now
To get rid of the *.pfb, *.pfm and *.ttf files in C:\Users\MyName\AppData\Local\Microsoft\Windows\Fonts go to the registry and remove all references to them in "HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\Fonts" and "HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\Type 1 Installer". Then reboot. Then you can delete those files.