Downloaded that file for Win7, also Gpg4Win. Mentioned .asc file did not accompany Tor, in spite of the description on the Torsite. Other ways of verification I could not find. 
Nevertheless I followed the description involving Gpg4Win under "How to verify signatures for packages" via cmd.exe, it did not work. 

How can I verify Tor Browser?
Thanks a lot for your suggestions!

PS:Gpg seems not to be in English available?