While I am trying to build C# template assembly using Web 8 Content Management DLL and .NET framework 4.5, I keep getting "ContentManagement" name space not found error while compiling the application. Once I change my framework to 4.5.2 the issue resolved. I didn't get the issue for delivery DLL. Is Web 8 built on .NET Framework 4.5.2?Is it mandatory to use 4.5.2?
Yes, it's built on 4.5.2 and thus it is mandatory to use 4.5.2 or higher.
This is listed on the Prerequisites for client-side APIs and Web application extensions page in the documentation, which is part of the broader Prerequisites for this release section of the Web 8 documentation.