Could I bike 9 mile a day home from work starting with no current exercise?
I agree with the comments that 9 miles is a not a short ride for somebody not in shape, but you’ll get in shape for it really fast, so you should go for it. Just get ready to be sore in funny places for a couple weeks. 

You can make your situation better by doing a few things:


Buy a road bike instead, assuming you’ll be on pavement. At the very least, replace your mountain tires with something smaller, in the 30–40mm range. Mountain tires will slow you down and make you work harder. So will a heavy steel bike. 
Get a rack for your bike and buy panniers to haul your stuff. Wearing a backpack for 9 miles will get old fast. Whatever you do, don’t get one of those hip shoulder bags. Chiropractic disaster. Best is to get a bike with in-frame attachment points for the rack – many road bikes don't have these, so make sure to check before buying.
Get the bike and do weekend rides to get fit before using it for work.


Good luck, have fun, and be safe!