I was also looking for office pranks ideas for April Fools and this is what I found so far:
Stick a post-it note under your coworker's mouse so that the paper leaf covers the mouse laser. It won't work anymore.
Hang signs around the office that say, in big bold letters, "Now Under 24-Hour Surveillance."
Text your coworkers pretending to be their boss and tell them to be at work 30 minutes early today for an urgent meeting.
Tape this sign over the printer, and make the IT department say the printer is now voice activated. Watch people scream at it, when it doesn't do a thing.