Within Master Drafting there's a 2D Clean option in the file menu and under that you'll find Purge Symbol.
To move geometry from one Drawing to another the easiest way is via a symbol.
Define Symbol
Select Entities (max 10,000)
Define Origin
Name Symbol
Export Symbol
Into New Drawing and
Create Instance
Select file icon and find your exported Symbol
Locate origin
Smash Symbol if you need to get back to the individual entities.
With the drawing open in Master Drafting,
Go to File, Clean2D
Run the Clean by clicking on all of the buttons one at a time, top to bottom using the default settings given.
The following cleans up the drawing size dramatically:
File, Calculator,
In the text box type: "L V" (enter)
-this outputs a log to the list window of all variables attached to the drawing.
In the same text window type: "delete all"
-this will remove all of these variables except the ones listed with an * in the name.