Information regarding importing DLL

can i import dll file of .NET in XOJO.?

See http://www.xojo.com/blog/en/2014/01/accessing-net-code-from-xojo.php

this example shows that how i create a component & then used it in xojo. Is there any process to use existing dll file directly in XOJO Project

Xojo supports ActiveX and a subset of COM. If your component adheres to that, then you can import it directly into your project and Xojo will create the necessary glue code to integrate it into your Xojo code. Otherwise, no, you cannot use it directly.