'From https://www.cadlinecommunity.co.uk/hc/en-us/articles/203139401
oDoc = ThisApplication.ActiveDocument

'Check to see if this is a part file
If oDoc.DocumentType <> kPartDocumentObject Then
MessageBox.Show("This rule can only be run in a " & DocType & " file - exiting rule...", "Cadline Community")
Return
End If

Dim oPartCompDef As PartComponentDefinition = oDoc.ComponentDefinition
Dim oNewParameter As Parameters = oPartCompDef.Parameters
Dim oUParameter As UserParameters = oNewParameter.UserParameters
Dim oParam As Parameter
Dim oValue As String

Try
oHoldingPositionName = InputBox("Specify the    N A M E    of the new Parameter *NO SPACES OR SPECIAL CHARACTERS*", "Cadline Community - Parameter Name", "New")
oValue = InputBox("Specify the    V A L U E    of the new Parameter", "Cadline Community - Parameter Value", "1")
oParam = oNewParameter(oHoldingPosition)
Catch
oParam = oUParameter.AddByValue(oHoldingPositionName, (oValue), "text")
End Try