.NET

[#1]

dan.glassman => thx man!

[#2]

<CommandMethod("Test1")>
Public Sub Test1()

Dim path As string = Autodesk.AutoCAD.ApplicationServices.Application.DocumentManager.MdiActiveDocument.Database.Filename.ToString

If Right(path,3) <> "dwg" then
MsgBox("This file has not been saved")
Else
MsgBox("ThisDrawing = " & path)
End If

Dim NewPath As String = Left(path, Len(path)-3) & "dat"
MsgBox(NewPath)

End Sub

[#3]

Imports Autodesk.AutoCAD.Interop
Imports Autodesk.AutoCAD.Interop.Common

Public Shared ReadOnly Property ThisDrg() As AcadDocument
        Get
            Return Autodesk.AutoCAD.ApplicationServices.Application.DocumentManager.MdiActiveDocument.AcadDocument
        End Get
    End Property


   Public Shared Function GetPath(ByVal ThisDrg As AcadDocument) As String
        Dim strPath As String = ThisDrg.FullName
        strPath = IO.Path.GetDirectoryName(strPath)
        Return strPath
    End Function