Without a commercial plugin that allows you to open and convert PDF to InDesign format you can only place PDFs as an image, and if the document is scanned you would need to run OCR before the text would be editable in any application.
I agree with Peter. Put simply, you can't. The way I would normally do this would be to OCR the scan within Acrobat or via an OCR website, and then put that copy into a new InDesign document.
Occasionally if I have to make an identical copy from a hard copy, I will scan it, place it into InDesign on a layer I call "trace" and then get to work on literally going over the top of the scan and doing my best to recreate it.
It's not a bad idea if this could be done in InDesign as a function of the software - it would certainly save the step of taking it into Acrobat and then bringing into InDesign only to trace it. It would have to use the same tech that is going into many of the Adobe mobile apps that are coming out...
That said, I have filed this as a feature request months ago. If others feel the same way, go to the wishform and make the request: Feature Request/Bug Report Form