I agree that the sentence (and the other one you posted) are proper or at least acceptable. There is some dispute among grammarians, however.
A better way to write the sentence would be "Filing rules must be learned to keep your files in order."
Type of sentence: To keep your files in order, the filing rules must be learned. (A) Properly constructed (B) Lacks parallel parts (C) Dangler (D) Misplaced part. I believe it to be (A)?
6 answers
Reed's sentence is far better than the original!
Maybe D) misplaced parts?
A is wrong
D is wrong
The answer is C dangler