is it possible to use the personal license bought from steam without opening it via steam? I mean, bought the personal version from steam and downloads the C2 from scirra site?
No.
The license systems are maintained independantly.
If you bought a license from the Scirra store then the license only applies to the non-steam version of C2.
The same is true for those licenses bought via the steam system, i.e. the license is only valid for the steam version of C2.