Hi Suzanne,
You can’t directly update your pdf as it’s more like a photo of your document.  You really need the word processing document.  Fortunately, there are ways to translate the pdf back to Word, which can be opened on your Mac with Pages.  If you want to give it a try, look for a free online PDF to Word converter.  The outputs are not consistently accurate.  I did this for someone else recently and found I already had a suitable app for doing that so I’d be happy to give it a try for you as well.  I can copy your pdf in your folder, convert it and send it to you directly if you like.  If the end result is usable, be sure to save it on your computer for next time.  I have a folder on my hard drive labeled ECIR and numerous folders inside it.
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