expression.AddBaseline(FileName)
expression Required. An expression that returns a Presentation object.
FileName Optional String. The full path of a file to use as the base line for this presentation. If FileName is not specified, then the presentation represented by expression is used as its own base line.
Remarks
This method generates an error if the presentation already has a baseline, or is a merged author document.
Example
The following line of code adds a base line to the active presentation.
Sub SetBaseline()
ActivePresentation.AddBaseline
End Sub