1.Try Goto Menu->PDF preview. In this, the Zoom button is switched on. Not very sure whether that helps. Please check.
2.There won’t be any zoom in/out facility in smartform.
The only thing you can do is in the smart style you can increase the size of the font for that particular content that is not coming properly.
Also you can try to check if the user run preview or print and decide which paragraph has to be used.
If user has choosen the preview you print the text using a paragraph with a “big” character.
3.Other alternative perhaps you can convert to PDF and using the PDF zoom functions.