Passing Form to DLL Method

Question

i hav a project with a DLL (someone created this),
suppose in this project a form (frmmain) contain some textboxes, combobox and some button also as save,Edit, delete..

suppose record loaded by ID- so he just call
objDLL.LoadRecord(this);
and record filled in text boxes and combobox, radio button

and clicking on save- programmer just call
objDLL.hndRecordSave(this); //// as form name is same frmMain

and record saved, record of textboxes, combo, radio, etc

similarly on edit he just call:  objDLL.hndRecordUpdate(this);
and record updated.

i just want to know in DLL how he manage all form in function and how he create this dll.
thanks hoping u all understand what i want to say.