C# build makes PDB files and obj folder

Under my project folder, I find the following folder:

Bin\Debug\

This folder has DLLs and PDBs files.

What are the PDB files and why do I need them?

I also notice the folders:

Obj\Debug\temp开发者_Go百科

Obj\Debug\tempPE

What are the above 2 folders? What is the purpose of OBJ\DEBUG folder?

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The PDB files are used by the debugger in order to give you a good debugging experience.
They should be left alone if you want to debug. When you build a release version, you will not need them.

The Obj folder is used during compilation time - you can delete it at any time, but it will get recreated when you next compile. If you delete it, the compile time (next time around) will be potentially longer, however. Leaving it in place allows the compiler to run more quickly in most cases, since it only has to reprocess some of your project, not all of it.