I finally worked it out today - the pdf had been downloaded from the city and when opened in acrobat, it was sideways. I had rotated it 90d and resaved before importing into AC. Apparently, that threw things off when creating the drawing pdf because I went back and re-downloaded the pdf, left it sideways and then rotated it once it was imported into AC. Now it plots fine.
I don't know why AC was rotating it 180d when plotting when I had only rotated in 90 in acrobat, but now that's it's fixed, I'm not too worried.
I have a related question though - the setting dialog for imported images, drawings, etc. has the filename and path, and choice of absolute or relative path, but if it's set to 'store in the project', are those irrelevent? I would assume that if it's stored in the project, I could delete or move the source file and the AC file would be unchanged - is that right?
thanks!