Once I download a file and unzip it, The Creality Print 5.1 is unable to locate it. Even though the file can be seen on the computer.
Is it the correct file format?
Hello @Robert_Beauchamp …! 
Welcome to the Creality Forum…! 
Most sites will download a set of files to a folder with different files inside depending on the site.
If you save a file to your desktop and go to File / Import / Model File it’s not there…??
It is showing STL
You may have downloaded the Gcode files. There are usually stl files but it looks like you have the stl file. If you double click on the stl file, does it open in CP?