1- Create and save your document as usual or open an existing Word document.
2- Go to "File" --> "Print" and choose the "Save as PDF" option at the bottom.
3- Give your file a new name and select a location for it to be saved in.
If the "Hide Extension" option at the bottom is selected go ahead and un-select it. It is nice to have the .pdf extension after the file name although in this context it will not alter the way your PDF file is created.
4-Voila! Your new file will now be smaller in size and will open only in Acrobat.
Tip: To make MINOR text changes after you have created your PDF file use the "TouchUp Text" tool in Acrobat.