Katana forgive me but I hijacked your picture and did some editing of it. The edits are now on my picture site and the bandwidth is mine.
My point in doing this is offer a less educated and less articulate point of view.
Why do you think this is a file knife?
Surely not from these marks?

If those were old file teeth they would taper and disappear from spine to cutting edge. They just appear to be tool or polishing marks to me.
Now these marks...

The heavy dark ones might be old teeth from some old crudely made rasp. The do appear to taper and fade...the cutting edge is on the right isn't it? But are we sure?
The cross hatching on the spine doesn't make it a file.
And if it is an old file, does that eliminate it's worthiness or does it point to a specific maker's technique and style who doesn't have access to a local steel supply house. Does it indicate a culture who lives where supply is limited and old tools are not discarded and replaced by a visit to Home Depot, but are instead used and reused however possible. Indeed a very worthy piece for any collection
My a less educated and less articulate point of view.