The fully qualified path of the document's disk file. 
   Namespace:   Autodesk.Revit.DB  
  Assembly:   RevitAPI  (in RevitAPI.dll) Version: 2015.0.0.0 (2015.0.0.0) 
Syntax
Remarks
 This string is empty if the project has not been saved or does not have a disk file associated with it yet. Note that the pathname will be empty if a document is detached. See  IsDetached  . 
 Examples
string docPathName = document.PathName; Dim docPathName As String = document.PathName