No you cannot have both *installed* at the same time, primarily because they both register as the default application for “.axx”-files.
However, you can run the portable/stand-alone version of 2.1 alongside an installed version 1.7.
And to be very clear:
AxCrypt 1.x AND 2.x are both *offline* file encryption tools.
AxCrypt 2.x does NOT require to be online to encrypt or decrypt or do anything, *except* for the very first time you run AxCrypt 2.x on a PC. Thereafter you never need to be online again.