Dpkg .deb file - Not a debian format

I'm new at Linux, so the following question may sound trivial. At the moment I want to install a .deb file, specifically the Cuda Toolbox 8.0, and it uses a .deb file. However, when I use the command

$ sudo dpkg -i cuda-repo-ubuntu1604-8-0-local-ga2_8.0.61-1_amd64.deb

I obtain the following log:

dpkg-deb: error: 'cuda-repo-ubuntu1604-8-0-local-ga2_8.0.61-1_amd64.deb.deb' is not a debian format archive
dpkg: error processing archive cuda-repo-ubuntu1604-8-0-local-ga2_8.0.61-1_amd64.deb.deb (--install):
 subprocess dpkg-deb --control returned error exit status 2
Errors were encountered while processing:
 cuda-repo-ubuntu1604-8-0-local-ga2_8.0.61-1_amd64.deb.deb

The solution looks quite trivial, since it is a standard procedure to install .deb packages and it is written in the nVidia tutorial. But I'm not able to do it. Any help would be appreciated.

This error happens when your deb file is broken. Check if you have downloaded properly (use md5 or sha checksum).

I just had this error when I was trying to install a deb file when its download wasn't finished yet.

$ sudo dpkg -i rocketchat_2.9.0_amd64.deb 
dpkg-deb: error: 'rocketchat_2.9.0_amd64.deb' is not a debian format archive
dpkg: error processing archive rocketchat_2.9.0_amd64.deb (--install):
 subprocess dpkg-deb --control returned error exit status 2
Errors were encountered while processing:
 rocketchat_2.9.0_amd64.deb