Currently the PC version is on 1.4.1 while Mobile still seems to be on 1.4.0, so crossplay is currently not possible unless you can downgrade the PC client. As far as I know that is only possible if you have the version released on GOG (they keep some of the older versions around).
I don't recommend that option. You can never be 100% certain there aren't anything nasty riding piggyback. If you still have to, I recommend using scanners like VirusTotal to check it first. Even then it's not completely safe but it's better than nothing. The war has unfortunately been lost. Only whitelists remains as a viable option.Well, if it doesn't work out legally, there is always a torrent.