5.82
Attention: Terrain must not be moved!
1st step:
Place PDF correctly and activate Orthophoto window
Step 2:
Go to Top View --> Right click in orthophoto window --> Remove orthophoto "gray" --> "Calculate orthophoto" --> Place red area in new window and click "Calculate".
Step 3:
Go to 3D View --> Activate Terrain --> Set Texture Type to "Ortho ext." and select newly created orthophoto.
Result: PDF which is integrated in orthophoto on terrain