The following function returns the file extension only.
eg. using the following function
GetFileExtension(“c:\test\file.aspx”) will return “.aspx”
Here is the complete function, copy and paste it in your form or a module
Function GetFileExtension(ByVal sFilePath As String) As String
' Dim fullPath As String = "c:\MyDirectory\MYFile.txt"
Dim sExtension As String = IO.Path.GetExtension(sFilePath)
Return (sExtension)
End Function