How to generate Assembly drawing in Altium
It can be somewhat automated, but it is tedious to do the first time, because you have to modify all your footprints

What I do is 


Rename two mechanical layers as "Top Assembly Dwg" and "Bottom Assembly Dwg". 
Desginate these two layers as a mechanical layer pair. 

Now anything on "Top Assembly Dwg" will get flipped to "Bottom Assembly Dwg" when you move the part to the bottom side of the board.

On each footprint, add the text ".Designator" on the Top Assembly Dwg layer.

Place this text centered on the part, and sized so that your maximum length designator (maybe 4 characters) will fit within the boundaries of the part.
You might also want to copy some silkscreen features onto this layer because you won't want to make prints that contain both the Assembly Dwg layer and the silkscreen layer.

Make a PDF output that prints each of the Assemlby Dwg layers, along with whatever other layers are appropriate to make your assembly drawings.


Altium will automatically replace the ".Designator" text with the actual designator when you generate output.