Ctrl+Enter should insert a hard page break in the document. You may not "see" it if you have the document in Draft layout. There are a couple of things you can do to "see" the page breaks:

• Put the document in Print or Page mode. I use Alt+Ctrl+P, but you can also use the little icons at the bottom on the screen in the status bar.
• Turn on formatting marks. I use Ctrl+Shift+*. You should see a page break indicator.

These page breaks should be retained when the document is saved as a PDF.