Looking to create a script to query all computers in a .txt file (pulled from AD) to see if a path on C:\ exists. From that I would then filter out the computers which did not contain that path, and then replace a file. The latter part to this I can do, it's the first part which is troubling me. I'm guessing Test-Path would be used, but can that be used to query a .txt file full of host names?

I would start by learning the basics of PowerShell and scripting.  We will not write your script for you.  Study the following and post back with a specific question about a script.

Start here: https://technet.microsoft.com/en-us/scriptcenter/dd793612.aspx?f=255&MSPPError=-2147217396