To transfer PDF files from your computer to your Nook, you will need your Nook plugged into your computer with the USB cord. You will need to make sure you have administrative rights on the computer you want to work from, so it is best to complete the steps from your personal computer!
Whether you have a PC or a Mac, the directions are essentially the same.
First, make sure your Nook is plugged into your computer. Open Windows Explorer (or Finder if you are using a Mac), and open the Nook drive and navigate to the folder: Nook\My Files\Documents as depicted in the picture below:
To transfer the PDF file you want to put on your e-rader, you'll need to find where it is saved on your computer. Right-click on the file to copy it. Go back to the Nook\My Files\Documents folder and paste the PDF file in the folder. When it has been succesfully copied, you'll see it appear:
To use the PDF on your Nook, open your library and sort by most recent. It will appear near the top:
If you're unsure of what e-book format is compatible with your personal e-reader, or if you want to know what devices you can use to read a particular file format, check out the Comparison of E-Book Formats from Wikipedia that details all formats available and covers virtually all devices. Wikipedia is updated frequently, so check back often!