Your story is a bit confusing because I think like a lot of people you are mixing up the password for a locked PDO file with the registration key that you need to buy to get the full features of Pepakura DESIGNER, but they are two very different things.
But for printing, it doesn't even matter if the file is locked or if you don't have the full version of Pepakura Designer. And you don't have to convert it to a PDF file to print it.
You can use an unregistered version of Pepakura Designer to print a PDO file as long as the designer didn't lock it (it doesn't have a password) for a bit more possibilities (if you want to change the way it was cut or change the flaps a bit).
You simply open the PDO file, and click print in the file menu like you would normally do. That's all, and you can even use the print button if your Pepakura Designer is unregistered.
If the file is locked, you simply have to use the Pepakura Viewer, it is totally free and can even open and print locked PDO files (you just can't edit them, because it is only a viewer.
I don't know about your PDF converter problems if you still really want to go that way, because all you should have to do is install it, and then before you print, instead of your regular printer select your PDF printer, and then when you click print, it should ask you to save the PDF somewhere. Is there anything in the print preview or is it also blank? If the PDO doesn't have textures but is just white, make sure you didn't disable the lines and flaps.
