Hello,
If you get your pdf File from a Scan, you have "only" a Bitmap PixelFile, and you can use the imported pdf just as an Image.
You can not even snap to Verticies on the drawing, because there is no posibilty for Vectorworks to analyse the bitmap, and for example figure out if the Pixel belongs to a Text or a Line or whatever.
If you have a pdf File that was exported from a CAD Program, then VW can snap to Points and so on.
That's a briliant feature (I guess since VW2008) to scale Plans precisely, and measure and so on.
If you use the pdf image in VW as a Base, and draw your stuff on top of it, and export everythink to .dwg, then the pdf page will be a image File in NNN.dwg Folder, that VW produces.
The pdf Image is just refenced in the dwg File, and not incorporated like VW does.
This can cause some trouble with Autocad Users who open the dwg File, because as far as I know, they have to tell AutoCAD where the imagefile that belongs to the reference is located...
If I have to base drawings on a pdf, I put the imported page on its own Class, redraw everythink I need, and make it invisible.
Horst M.