Adobe Acrobat is a fine editing tool (if you enjoy being pestered with constant updates). But Mac users have a built-in alternative that comes with features comparable to the free version of Acrobat.
The list of ways you can manipulate a PDF or photo (including JPEG or PNG) in Preview is long. Here is just a sampling to get you started.
How to fill in and sign a form on Preview
This is the most basic function of a good PDF reader. In Preview, just click on the fillable sections and start typing.
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