From Visual Studio 2010 Tools menu, click Dotfuscator Software Services as shown in the figure below.
This will start the obfuscation service. Once you start building the application/library the following form will come up.
Right click Dotfuscator1 tree node and select “Add Assemblies”
Browse the assembly you want to obfuscate.
Once you have selected the assemblies, build it using the Build Menu. If there is no error, then the new output will be obfuscated.