Why can't Opera manage to include an easy, effective pdf converter? Go visit Firefox's add-ons, they have dozens. You add them, an icon comes up, and you simply click on the icon to save the whole frickin' page - not just the frickin' screen - but the whole page. Because screen shots suck at this.
Opera itself can open PDF documents. I just tried that and it works. You can also save as PDF from Print.
You can press CTRL+P in Opera and save the whole page as PDF easily by Save as PDF tool.
Alternatively you can use any available PDF printers such as Microsoft Print to PDF in Windows.
Note: The addon you asked is not PDF converter. The term "PDF converter" indicates document conversion, such as from DOC to PDF.