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
In the C:\Users\MyName\AppData\Local\Microsoft\Windows\Fonts directory right click on your font file and choose "Install for all users" (translated). A prompt will show up, telling that the font is already installed. Still click "Yes". The font will then be copied to %WINDIR%/Fonts.
One might think that the font file in C:\Users\MyName\AppData\Local\Microsoft\Windows\Fonts is not needed any more and can be deleted. But when you try, a message pops up, telling that the action could not be finished as the file is opened in System. - So we just have another copy of the file.
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.
You just need to right click on your font file and select install font for all user.
It will be visible in every apps then.