The PDF Catalog generator would be found on the left side of your screen on the products tab.
Click on PDF Catalog (top right corner) -> Build PDF Catalog
On this screen you must select the different options to generate your PDF. After doing so, click on GENERATE and that will show you the preview of what the PDF catalog will look like. When you are ready just click on EXPORT TO PDF.
After clicking on GENERATE you will see the cover page for the PDF. You can edit the info there if you need to. At the bottom you will see the preview of the catalog.
To export the PDF catalog click on EXPORT TO PDF. Be sure to use the software you would like to open the catalog with. After clicking OK your PDF catalog will be displayed.