Can I add a an automatic door bottom (ADB) if the door is mortised and the door edges are fully intact?

Yes.   If the door is fully mortised,  then a hole can be drilled in the edge of the door for the plunger and nut to be exposed.

The brass plunger nut can be threaded out by hand for enough exposure to reach the frame.

In short,  the brass plunger nuts can be adjusted outward to give more tension on the unit, as long as it does not come off of the interior rod.

There is not a specific "maximum adjustment" that can be defined.   1/2"  to 3/4" would be approximate values.

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