application used to open a file on imac

my wife was trying to open a pages file on her new iMac. The file wouldn't open. It allowed her to try to use another application. She chose Stickies. Don't ask me why. Of course it didn't work but now it seem Stickies is the default application for ALL her pages files. Nightmare. How can I reverse this? I can open individual pages files by using Option/Click and then choosing pages. The files open but immediately divert back to Stickies when I close them and try to open them again. There must be a way to correct this. Please help