There are times when base information that you wish to work with in a GardenCAD drawing environment comes to you in the form of a PDF file. The PDF file format was developed by Adobe and is not a vector based file format like GardenCAD's .Vec or dwg/dxf used by AutoCAD.
You can work with a base map in PDF, but the PDF file first needs to be converted to a format that GardenCAD recognizes. The simplest approach is to convert the PDF file into a jpeg file and use the place Raster image tool and insert into a GardenCAD drawing file.
A Google search reveals many tools. Some are online - you upload the file and nominate a resolution, others are applications that need to be installed.
If you have installed Photoshop or GIMP on your PC, these can also be used to convert a PDF file to JPEG.
The Mac operating system (OS X) can also be used. A tool called Preview (found in your applications folder) can be used to convert PDF to JPEG.
Tip: set the resolution of the output to 72 dpi (or possibly 150 dpi) or the file size will be too large.