Load web page in Opera for Android. Then in left corner of adress bar you will see "+", click on it and choose "Save for offline".
In a speed dial there is "Saved pages" icon and there are all of your saved pages for offline use.
If you want to export pages, you should have rooted phone and install some file manager who can open root files.
Then go to "/data/data/com.opera.browser/app opera/saved pages". There is all your saved pages, in .mhtml format (shortly .mht). It is Microsoft format which can store complete web page (html, scripts, pictures etc.) in one single file.
You can move/copy pages to anywhere in your phone or PC, and open it with Opera or many other browsers who support .mht files. Also, many browsers or freeware software can convert .mht to .pdf, .doc., .html etc.