How to edit a pdf file?

I am emailed two pdf files once per month. I need to somehow edit these files. I have no idea how this can be done?
I did figure out that I can convert a pdf file to word using this website: https://www.pdftoword.com/
and then using MS word convert it back to a pdf.

Can someone suggest other ways to get this doe? Is their just one piece of software I can but that will let me edit pdf files directly?