User1 has Adobe Reader X installed, fully up to date.
User2 has Adobe Acrobat X installed, also fully up to date.

If User2 creates a PDF (either using Word 2010 or Acrobat) and sends it to User1, User1 will see additional annotation tools such as underline, record audio, stamp etc. aswell as the drawing markups toolbar. This happens desipte the relevant options being disabled.

If User1 creates a PDF (using Word 2010), the PDF won't show the additional annotation tools or drawing markups toolbar for User1, but will for User2.

If User2 creates a PDF (again, in Word or Acrobat) and sends to User1 for annotation, then User1 sends back the PDF with the annotations to User2 who opens the PDF in Adobe Reader, the annotation tools and drawing markups toolbar don't appear, but do if User2 opens the PDF in Acrobat.

I really hope that makes sense.