First select a Unicode font such as Cardo or Lucida Grande.
Then select Paste Special from the Edit menu, and Unformatted Text from the submenu (not Styled Text).
Word also supports right-to-left entry of Hebrew, but not editing of the text.
You can create and edit text in Accordance, Mellel, or TextEdit, and paste it into Word.
PowerPoint on Mac does not support Hebrew Unicode, even when pasted from Word.