KB00083 - How do I open .sti files?

...and what about .ssk files as well?

Files with a .sti extension are saved individual stickies, and .ssk files are skins which alter the appearance of stickies. .sti files are created by right-clicking a sticky title bar, and choosing "Save As...", but then double-clicking those files might not open them again.

Set a file association from Stickies by opening Settings from the notification area icon, and on the App tab, make sure that "Associate .sti and .ssk files with Stickies" is toggled on.

If the is already on but double-clicking .sti files isn't working, you might like to try switch it off, and then on again, as that will recreate the file association, and fix any problems.