About the updates: If WordPad won't open it as originally downloaded, then the file probably isn't a Word document. There's nothing you can do about that.
I can't tell from your question whether the original file type extension was ".docx" or not. If the file was compressed into a zip, tgz, rar, 7z or other archive format, then you'll need to use a program to extract it.
If it's a self-extracting .exe, the program is included...but a tool like the free 7-zip utility will usually let you open and extract files from a self-extractor without having to trust the executable part.
A bit of warning: The .docx file is actually a .zip file internally; so if you open the file with 7-zip and see a bunch of mystery files in folders with names like "word", "docProps", "customXml" then you really do have something that is or at least was a .docx file. In this case, your renaming might not work unless you turned off extension hiding (or did the rename in Command Prompt, which doesn't do any "user-friendly" drek.)
If that last bit doesn't sound familiar, try this. Go to Control Panel>Folder Options (or the Folder Options dialog in the Tools menu of the file explorer, if it's there) and on the "View" tab make sure that "Hide extensions for known file types" is unchecked. Then do your rename.