this might be useful:

https://jeremylindsayni.wordpress.com/2016/04/02/how-to-read-and-create-barcode-images-using-c-and-zxing-net/

and

https://stackoverflow.com/questions/17512059/how-do-i-use-zxing-net-in-my-visual-c-sharp-form

it doesn't look like you have to be an expert in .Net, but watch some youtube videos on how to create a solution / project for creating a DLL. Choose one of these project types in Visual studio or something similar in SnapDevelop:

I don't have a scanner, so it won't be easy to help you, maybe someone else could help on zxing's githbub?
https://github.com/micjahn/ZXing.Net
They also have some example I think.

You should create a ".net class library" in C# (or Visual basic .net) and then use the DLL import tool of powerbuilder.

have fun!