To get PDF to display properly on your screens, any mobile screen, you have to have TAGS turned on when you create the PDF. They are turned off by default, which is nutz.
If you create PDF from WORD, you have to go to the menu bar initially, pull it down and choose configure settings. Click through all the tabs and find the tag boxes to select.
If you create PDF from the web, do it from within Acrobat and choose settings in the 'create PDF from a web page' dialogue window. I am not giving you the exact names of these items because I dont have Acrobat open. Mac and Win are slightly different below ver 8.
But searching the help doc for turning on tags should help you.
What tags do is follow the text thread so that if there are two or three columns, mobile units can break it down and display as one column accurately.