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1. Open the file with Acrobat.
2. Document-> Edit PDF-> Add Text, drag to create a text box, then enter your text; or just place the cursor where you want the text to be and start typing.
3. You can choose font type, font size, font color with the right hand side FORMAT panel. But you can't change background of the text box.
4. You can also decide whether you want to have a bounding box for the text by checking the Showing bounding boxes at the lower right corner. 
   
5. To delete a text box, click Edit that is next to Add Text, then click on the text box, hit Delete key on the keyboard.

Using InDesign - more flexible and powerful. For instance, having background color for text box, different shapes of text boxes.

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