In Sweet Home 3D, you can just import the image displayed behind a plan at JPEG, PNG, GIF or BMP format to help you draw faster walls and rooms upon it.
If I accepted to support PDF, reusing the image it contains to display it wouldn't be too difficult, but recognizing the meaning of the different drawn lines in the PDF would be much more tedious (how could the program recognize a wall? How could it recognize a line is wall and not a dimension line or an other type of line...).