How strange! PageUp works just fine when you browse your document in Print Preview mode at Microsoft Word, but not the PageDown key. You are still able to move forward only by pressing Ctrl+PageDown, but you don’t want to use a shortcut when you can press just one key.

Your keyboard is (most probably) fine, and you don’t need to adjust any Word settings — just try to increase the size of Word. Put the cursor of the mouse at a corner and drag to increase the window of Word.

This PageDown problem is caused when the pages are a little larger than they should be.

Instead of enlarging the Word window you can also open the Zoom settings and make the preview pages smaller. Enjoy!

Being yourself an author or student you will perhaps appreciate especially this feature, that the very structure of the book will teach you how to work. The book contains even chapters on how to prepare a document for professional publishers such as Amazon. Reading Steven Adams' Writing a book or thesis in Microsoft Word you are surprised realizing it makes you want to work -- to think, write, use Word and be creative!