Thank you for the detailed description.
Prepare form tool is a part of Acrobat Pro. However, Acrobat Reader is open on the screen, which is freeware. It doesn't include the Prepare form feature.
There's likely a chance that when you select open with Acrobat Reader is set up as the default app to view/open the PDF file.
As you are an Acrobat Pro user, we suggest you uninstall the freeware Acrobat Reader.
Or set Acrobat Pro as the default PDF viewer from the above screen. Open With>Choose another app> Select Acrobat Pro >check "Alway use this app to open .pdf files.">OK
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