I agree with Andrew, however ensure that you save the building block in the document template rather than the default normal template if anyone other than yourself is to use it.You can use the following to insert your autotext building block in a bookmark.
Code:
Sub AutoTextToBM(strbmName As String, oTemplate As Template, strAutotext As String)
'Graham Mayor - https://www.gmayor.com - Last updated - 10 Apr 2019
'strBMName is the name of the bookmark to fill
'oTemplate is the template with the autotext - probably ActiveDocument.AttachedTemplate
'strAutotext is the name of the autotext entry
Dim oRng As Range
On Error GoTo lbl_Exit
With ActiveDocument
If .Bookmarks.Exists(strbmName) = True Then
Set oRng = .Bookmarks(strbmName).Range
Set oRng = oTemplate.AutoTextEntries(strAutotext).Insert _
(Where:=oRng, RichText:=True)
.Bookmarks.Add Name:=strbmName, Range:=oRng
End If
End With
lbl_Exit:
Exit Sub
End Sub