In simple terms, a Crdownload file is a fragment of a larger file that was being downloaded. It's not a complete file, so you won't be able to open it like you would a normal file. Instead, you'll need to wait for the download to finish or find another way to obtain the complete file.
Completing the download is usually the easiest way to deal with a Crdownload file. If you restart the download, Chrome should pick up where it left off, and you'll end up with a complete file. Alternatively, you can try to convert the file to its original format, but this can be a bit more complicated.
