Guys, I always used a screen capture program to import my PDFs into Sketchup on Windows (Mac does it out of the Box). I had a large set of PDFs that would have taken too long to do individually so I did some research and came across this program http://www.pdfjpg.com/register.html
It does cost $30 USD however it works fine and does multiple PDFs and adds them into their own folder. You can use it for free by clicking "Start Converting Now", it will open up a buy page which you can simply close, you will notice that the files will be created in a folder which automatically opens. You can then drag and drop the files straight into PlusSpec or use file import. Note, if you want higher resolution image input, go to teh Sketchup Window menu, Select preferences, Open GL and tick "Use maximum texture size"
Note each image you import will add file size. In my use case I found, each image was under 2 meg, If i imported all, i would have a 10 meg file before I draw a line, so you should really only import what you need. You can also delete these images and purge the model once you are finished with them.
I also have at tip that may help a lot of people who always works from A3 drawings.
Basically I set up a template that has an A3 sheet outlined and dimensioned at 1:1 scale. This could be used to screen captured and printed to scale before going to layout. I would use this type of template for many things including tracing over a drawing that has been produced in A3 so I can quickly draw it in PlusSpec. The benefit is the imported PDF screen shot will be very close to scale. I'd always use the
to double check.
Here is the download, I hope it helps.