A bench grinder works well. I hold the left side edge against the wheel and roll it up, then repeat on the other side. The cutting edge must be higher than the back.Having both cutting edges the same is a bonus.
There is also a special grinder with a jig just for drill bits.
I have used my 4" hand grinder with fair results. I clamp it in a vise with wood spacer blocks, turn it on and pray .
I also prefer my bench grinder. But with a file I would clamp the bit in the vise and just try to keep the angle on the edge as close to original as possible. It's gonna take a bit longer to do than with a grinder.
If you use a lot of drill bits a drill doctor works well, sold at Lowes and Amazon, I never heard of someone using a file as they are about the same hardness. I always keep a lot of 1/8 in bits to drill a pilot hole before using a larger bit which saves time and your larger bits. I would try emery cloth if there wasn't a grinder available. I find a disk grinder works better than a bench grinder. One advantage of sharping your own bits is you can change the cutting angle to match the material you are drilling.