A Partial Download is a file created by a file sharing or download program to store incoming data. As the name suggests, this is only PART of the original file, as the download hasn't finished yet. What you can do with it depends on the type file being downloaded.
If it is a video or audio file, you may be able to rename it to a .MP3, .AVI or .MPG, for example, and then use VLC Media Player to play the part that has been downloaded (this may or may not work depending on how much of the file has been downloaded).
To view whatever raw data is in the file, we recommend using EditPlus.