Your yard must be about 10 square feet if you got 3 seasons on that blade. Mine will look like that after one mowing due to all the rocks and crawfish/ant mounds that I have to mow over plus I mow over 6 acres so that is a lot of grass to cut .
I wouldn't sharpen it yet if I were you unless you already have it off the mower, then just a little touch up on the last couple of inches should do it.
I do have some files, but they aren't used to sharpen anything. I cant believe anyone with a mower doesn't have a 4.5" grinder. They are such a handy tool. With cutoff wheels, they can be used for cutting off steel or with abrasive wheels, sharpening/shaping etc. A harbor freight 4.5" grinder can be had for under $30 for the top of the line model with paddle switch. For lawnmower blades, I like to use the sandpaper grit wheels (some folks call them "tiger paws") rather than a hard abrasive wheel. It gives a smoother surface and doesn't gouge like a hard wheel can but sharpens very fast. I would use a hard abrasive wheel if I was working on a bush hog blade since you would need to remove a lot of metal.