AutoDesk sells a product that takes RASTER IMAGES (JPG,TIF, etc) and treats them as NATIVE AutoCAD entities. They're really still BITMAPS, but it RASTEREDITS the drawing, making only the changes you want, can blank out stuff like title-blocks and erase smudges, and YOU DON'T HAVE TO REDRAW ANYTHING but what you want to! We used the product with HUGE success years ago before ADESK bought them out, and it LITERALLY opened up our ENTIRE VAULT of Scanned TIF images ! I don't recall the product name now that its owned by ADESK, but they offer it on their web site as a purchasable product.
On the PDF thing- I just
INSERT OBJECT-PDF into ACAD, reposition it, rescale it, and go from there, if it doesn't have native vectors. Even Bitmaps if they were scanned well look FANTASTIC, and as long as either the save-path to the bitmap PDF always stays the same (vault folder, etc) or the bitmap PDF stays in the same directory as the ACAD drawing you inserted it into, you're good to go.
It can even be used as a tracing underlay.
Otherwise, if there are native vectors you can either extract them to dxf (fine choice - editable, of course) or insert the PDF directly. It'll show up beautifully, but of course you can't edit it. This is really valuable only if you need a PDF image as a detail in your drawing, and don't want to redraw it or ever expect to need to edit it. Otherwise, convert the PDF to vectors via your favorite DXF converter. If you HAPPEN to have ADOBE ACROBAT, you can even select layers in the PDF you want on & off .
If bitmap only tho, either insert it as an underlay and trace it or get that ADESK product I mentioned above.
GOOD LUCK ! Let us know how it goes !
C. Fee