i well find help
https://www.ghielectronics.com/downloads/man/Library_Documentation_v4.1/Index.html
But I can not find the DLL file.
Library where I get it?
Please, you’ve gone a bit random on us 
Stop and tell us what you have got and what you’re trying to get working. We can help guide you to make sure you get everything you need.
As a starter, this page .NET Micro Framework – GHI Electronics has the install items you need. It also has links to the correct library references for both GHI’s 4.2 extensions and netmf - you can also find 4.3 info there if you need, and the legacy 4.1 stuff if you really want it (unless you have a Panda or Domino, you probably don’t)