Range.InsertAutoText method

Attempts to match the text in the specified range or the text surrounding the range with an existing AutoText entry name.

Namespace:  Microsoft.Office.Interop.Word
Assembly:  Microsoft.Office.Interop.Word (in Microsoft.Office.Interop.Word.dll)

void InsertAutoText()

If any such match is found, InsertAutoText inserts the AutoText entry to replace that text. If a match cannot be found, an error occurs.

You can use the Insert method with an AutoTextEntry object to insert a specific AutoText entry.