If you have a PDF file with good resolution, you can import that as a Vector PDF, which can provide a more precise background and snapping points. Importing a scanned image or file with poor resolution may not produce a successful result. 

To start, access the Vector PDF extension tab from the Show all tabs drop-down. 

Load the PDF into the drawing

1. Click on Load vector PDF. 

2. Move the cursor to the drawing area. An image component is now attached to the cursor. 
3. Place the frame in one of two ways: 
   • Left click once to set a starting point, then move the cursor until the frame is the desired size (without holding down the mouse button) and click once to set the ending point.
   • Click and drag the frame to make the desired size. 
4. Release the component by moving the cursor outside the drawing area or pressing Esc on your keyboard. 
5. Double-click the frame to select your PDF file from the Open dialog box and click Open.
6. Select which Page to import and click Insert.
7. From here you can either select additional pages to insert or close the PDF import window.

Measure and scale the PDF

1. Click on Measure and scale.
2. Move the cursor into the drawing area. A blue line with a dimension is attached to the cursor. 
3. Find a known distance in the drawing, such as a dimension or doorway. Left click on the starting point of this distance, then drag the cursor and left click on the ending point. Be sure to have Graphical Snapping turned on to accurately select the points.
4. Enter the actual length in the green box that appears at the cursor and press Enter on your keyboard. 

You may not notice a shift in the view, but the PDF is now scaled based on the length entered. You can use the Ruler tool or a dimension to verify the sizing.