Open AutoCAD, netload dll, select list of files, audit each one without opening them in AutoCAD, saveas.
Well, you're actually opening them in AutoCAD, it just depends whether you want it to open them graphically or not and judging by your response, not.
Okay then, not graphically, which means you're reading in a DWG file and it will NOT have a Document object associated with it. You will find, as I suspect you already have, that batch processing drawings, even in the editor, let alone non-graphically, is not such an easy thing, especially for somebody who's new to this.
Having said that, as I understand you're requirements, you have the following choices:
1. I think ScriptPro is still shipped with AutoCAD (you will have to check), so you could be able to use it to write a script that audits, purges and binds, across a selection of drawings. This can have problems ie. audit hits something ugly and crashes is my first thought. Second, purging might not get everything - it did require multiple passes in previous releases; not sure now. As far as binding goes, well that's a subject I've commented on extensively on this board - search.
2. Write a .NET program to Audit, Bind and Purge - not particularly easy if you really want to make it robust. Binding has it's own issues - see point 1 above. With respect to purging, yes you can do it, as has been shown on here recently by Gile I believe, if memory serves, but you have to be meticulous. As far as doing an Audit goes, yes, you can reference the AutoCAD COM type library and use it in your .NET code (one of the features of .NET and it's compatibility), but I don't know if that would even work if you're opening a drawing as a database (ie. non-graphically), as the ActiveX documentation requires a Document object from memory for the AuditInfo method, which you won't have, if you read the drawing via ActiveX's ObjectDBX's methods.