Adobe PDF is postscript page description format that may be viewed by Adobe's acrobat reader. The reader application is available for many operating systems. This is a vector description format--not a bitmap format.
The middle popup menu provides a selection to export just the visible graphics and text, or the entire drawing.
Use the right most popup menu to chose a background option. You may choose no background, white or black and whether to include the Grid in the output.
Use the save button to execute the save action after all parameter selections are made.