Microsoft Word & Microsoft Works are separate programs, both are provided (sold!) by Microsoft.
Works is, as I have always understood it, a "cut-down" version of Word. (certainly is costs less.)
If you previously had MS (ie Microsoft)Word on your computer you presumably have a disk containing this program and, as VoG™ said, you need to install that program from the disk.
If you had only MS Works then similar applies.
Word was usually supplied as part of MS Office and you will certainly have a disk for that if you had it installed previously.
I've never heard of a progam called Microsoft (MS) Document. Do you mean will you be able to open documents currently saved in "My Documents"? "My Documents" is simply a folder - it isn't a program that you can put on your computer; but if those documents were written in MS Word you WILL be able to open them when MS Word is re-installed; similarly if they were written in Works - when that is re-installed you will be able to open those documents. BUT as far as I know and in my experience you cannot open Word documents with Works.