To upload to K4PC, you can put MobiPocket ebooks in My Documents\My Kindle Content. However, it only supports MOBI ebooks.
The Kindle for PC and the B&N PC Reader do not support PDF.
You can get an idea how PDFs will look on the Nook using the ebook viewer that is part of the
Sony eBook Library. This is because both Sony and B&N use mobile Adobe Digital Editions for PDFs and ePubs. The actual reader will also have a landscape mode.