First download the software of “verypdf pdf editor” in www.verypdf.com
Its icon is this:
Then open it, and click “open” and add a pdf file in, below is the illustration:
Then the new picture is below:
Choose the toolbar of “edit content” and click it, then two icons will light abruptly, below is the illustration:
choose the icon “T+” and put your cursor in the pdf space and click left-button of your mouse, a dialog window pops, then you can edit, below is the illustration: