BookBuilder creates LBK files that can be viewed in PocketBible for Windows Desktop. You just need to place them in the correct folder.
Your books should be placed in the same folder in which PocketBible keeps its other LBK files. The easiest way to find this folder is to run the Cloud Library app from the Laridian folder in your Start menu and select Help. Half-way down the screen is a list of folders where PocketBible searches for installed books. While you can use any of these for your books, it's best to use the first one listed there, which will probably look something like C:\Users\[username]\AppData\Roaming\Laridian\Laridian Books.
Once you've copied the book to that folder, exit PocketBible if it is running and re-launch it so it will recognize the newly installed book.