I just tested (we never do this in PDFs from CAD files) and it is not; however, if you use Bluebeam Extreme, you could use OCR to recognize the text first, then it would be searchable.
Additionally, depending on which PDF writer you are using, you can substitute SHX fonts with TTF fonts when there are exact matches available. The built in DWG to PDF writer appears to have some ability to do this by selecting the Capture All option under Font Handling in Custom Properties.
In our case the question becomes is it more important to be able to open the file in under 45 minutes (yes we had a file that was taking that long because of TTF fonts being used in the xRefs) or is it more important to be able to search the PDFs? Our vote was for faster opening in this case (down from 45 Minutes to approximately 45 seconds)