Relative path to source code files

How can I add Fortran source code files from different directories to my project so that these file references will be saved in the project file with relative paths? When I add files in Visual Studio using Add → Existing Item, the absolute path of the files is stored in the project file.

When files are added to a project they are added as full paths. In order to maintain a project file with relative paths it is neccessary to edit the project file by hand. Its fine to do this and the relative paths will be preserved in the file. Make sure you use double backslash when specifying file locations.