As part of a recent homeowner project, I applied a file to dull pruning saw that, as far as I can recall, Came With The House™ and has been untouched for decades:
Yeah, that’s a lot of steel filings; it was really really dull. Notice how they’re neatly lined up toward the blade?
It looks better from the side:
Despite my crude technique, it cuts wood like a hot knife through butter.
The Smell of Molten Projects in the Morning 
Good work, I remember my Grandfather sharpening saws for use on the farm, the saws were always kept sharp.
Probably almost a lost art today, bur was taught how as a kid, step one sometimes was to put a very large file on a flat surface and run the saw teeth over it a few times to get all the teeth the same height, then hand file down to where the flat spot just disappeared, then finish up sometimes with a teeth setter to make sre the proper set was on the teeth so the saw did not jam.
I should have done that, but it was in such bad shape anything, even my crude filing, was an improvement! [grin]