Is there a quick way to reduce the size of a document (pdf or Word docx format) to a half page?

I have an 8 1/2" x 11" poster that I created in Microsoft Word and converted to pdf format to upload to my website, but I would like to have a smaller half-page version of the poster to use as a bulletin insert, or program insert. I am under a bit of a time crunch, so any help I can get will be much appreciated.