Use dumpbin command-line.
dumpbin /IMPORTS <path-to-file> should provide the function imported into that DLL. dumpbin /EXPORTS <path-to-file> should provide the functions it exports.Use the free DLL Export Viewer, it is very easy to use.
For native code it's probably best to use Dependency Walker. It also possible to use dumpbin command line utility that comes with Visual Studio.
If a DLL is written in one of the .NET languages and if you only want to view what functions, there is a reference to this DLL in the project.
Then doubleclick the DLL in the references folder and then you will see what functions it has in the OBJECT EXPLORER window
If you would like to view the source code of that DLL file you can use a decompiler application such as .NET reflector. hope this helps you.
For .NET DLLs you can use ildasm
Without telling us what language this dll/assembly is from, we can only guess.
So how about .NET Reflector
Use dotPeek by JetBrains.
https://www.jetbrains.com/decompiler/
dotPeek is a free tool based on ReSharper. It can reliably decompile any .NET assembly into C# or IL code.
You may try the Object Browser in Visual Studio.
Select Edit Custom Component Set. From there, you can choose from a variety of .NET, COM or project libraries or just import external dlls via Browse.
Source: Stackoverflow.com