Can anyone guide me to add the reference Teigha in VBA? I tried to download the reference from open design alliance website but could not figure it out.
you have to ask in Teigha forum (I am not sure whether such exists). Teigha is not product develop by Bentley, so you will probably not receive any answer.
It's also not clear what product do you use. You mentioned VBA (Visual Basic for Applications), which means you use some product that support this technology.
BTW Dod you try to use Google or Bing? I quickly found plenty of blogs and articles that seems to be related somehow to Teigha and VB (but today it's probably about VB.NET).
Labyrinth Technology | dev.notes() | cad.point
You can create trial account in Teigha and get 1 month access to Teigha forum.