Here's what you'll need to do:
Download the entire program you purchased to your computer.
Connect the Kindle to your computer via USB cable.
-It should appear in your file browser (such as Finder on Mac or Explorer on Windows) as if you attached an external USB drive.
Locate the "documents" folder within the Kindle.
-You can do this within your file browser by opening the Kindle icon/folder and then navigating to the "documents" folder.
Drag and drop the PDF file from the original location to the Kindle "documents" folder.
-If you have an older Kindle, you can still read the text from PDFs on your e-Reader — after you convert them. Amazon will do this for a small fee, or you can look for freeware utilities online. For newer Kindles, you may still want to convert the PDF so that you can take advantage of the Kindle's text manipulation features (like increasing/decreasing font size).
If you have any problems with the instructions above, you can visit this website for pictures of the steps: