You can just use Beyond Compare to compare the binary differences with two dlls but what if you need to find out what the differences are? You can do the following:
To compare two dlls to see if they are different:
1. Use Reflector to extract the contents of the dll into two different directories
2. Use Beyond compare to compare the two folder’s content (and its content)
This way, you can know which file, that is different and what the different is, when comparing two dlls.