User of Acrobat can save a created PDF with a specified "Initial View" which can include open magnification.
Acrobat provides access to the "Initial View" tab of the PDF's Document Properties.
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Adobe Reader does not have this capability.
However, you can override an "Initial View" magnification setting.
Open Adobe Reader's Preferences.
Select the Accessibility Category.
Tick the box/boxes for "Override Page Display".
Configure - OK out.
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Be well...