Point out areas in PDF And fill them dynamically

Hello, could someone explain what would be the workflow or tool that could allow me to indicate an area or field in a PDF to be able to fill it in a dynamic way?

The explanation given in topic 10 of the course I do not clarify this and as much as I try I can not get my purpose.

The PDF appears as an image.

Thank you very much, greetings!

When you are spying text in PDF, you are unable to do for particular field and it is selecting complete text in PDD correct?