I thought you just wanted to back up the file. To do that you could copy it into a folder for 'safe-keeping' and then if anything untoward happened you could just paste it back.
I'm not really up to speed with Opera so I don't know whether it has a bookmark backup facility, perhaps a trawl through their Help forum could give you a more definitive answer.
You could try to open the .adr file with Notepad. Right click on file and select 'Open with...' and then select Notepad.
Good luck!
Forgot to mention, you can open the .adr file with Notepad.