To open (or side load) PDF or ePub files in the NOOK for Windows 8 app:
Swipe up from the bottom of the Home screen and select Open File. This will display a file menu you can navigate to find the file you would like to open.
Tap or click on the file to select it.
Tap or click on the Open button to open it within the NOOK reader.
Once it is open, you can use some of the app reader's features, such as the Table of Contents.
Your document will not be displayed in the Library but will continue to be accessible to you using the Open File function on the app menu.
NOTE: The app cannot open or side load files that have security controls or DRM (digital rights management) associated with them.