Linking XML document into C# - few ways, that didn't work

I have a problem with loading XML document to C# Windows Phone Silverlight 8.1 project. I was trying a few ways, but there always was a problem. First way was (with problem):

XDocument doc = XDocument.Load(mypath);

Cannot open 'mypath'. The Uri parameter must be a file system relative path.

Next one was:

StreamResourceInfo SRI = Application.GetResourceStream(new Uri(@"mypath", System.UriKind.Relative));
XDocument doc = XDocument.Load(SRI.Stream);

Object reference not set to an instance of an object.

I don't know how to handle with it. I know this is a stupid question, because there is a lot of tutorials in web, but I always have this kind of problem with xml. Could you help me, please?