This looks to me like a file association problem. The exact solution depends on your OS, but in general it takes selecting the icon of one of your PDFs, getting info, indicating what proghram you want to use to open it, and choose apply the change to all files of the same type.
Right click on the file icon - then select Open With from the menu.
Don't select a program at this point - click Choose Program.
From the list of programs choose Adobe Reader (assuming it's there).
Make sure you tick the box that says "always use the selected program".
That should fix it so that PDF files always open in the correct program (Adobe Reader) instead of Microsoft Word