You can use Reflector, ILDASM or ILSpy to get the assembly version.
You usually can find ILDASM in C:\Program Files (x86)\Microsoft SDKs\Windows\v8.1A\bin\NETFX 4.5.1 Tools\ildasm.exe
(where v8.1A
is the version of the Windows SDK installed).
ILDASM:
![ildasm](https://i.stack.imgur.com/uTgYw.png)
Reflector:
![reflector](https://i.stack.imgur.com/yBFUC.png)