问题
There are different types of Class libraries available in Visual Studio such as Silverlight Class Library, Portable Class library and Class Library. What are the differences between these types? How can we determine the type of a Class library with File.dll file? How can we change a Class library from own type to another type of Class library?
回答1:
The Portable Class Library project type enables you to write and build managed assemblies that work on more than one Microsoft platform, whereas the "normal" Class Library project type doesn't.
"Microsoft platforms" include .NET Framework, Windows Phone, .NET for Windows Store Apps, Silverlight, Xbox; all in various versions or flavors.
Source
Go through this for converting from one class library to another type. (See also: this relevant SO question.)
来源：https://stackoverflow.com/questions/17379101/different-between-class-library-and-portable-class-library-in-visual-studio