Add the file to your deployment by right-clicking on the project and selecting "Add Existing Item". After it's added, click on it and set Build Action = "Content" and set Copy To Output Directory to "Copy always".
When you deploy it, it will be included, and you can access it like this:
string PathToRtf = Path.Combine(System.Windows.Forms.Application.StartupPath, "myfile.rtf");
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