If you are using Acrobat you can open a PDF's Document Properties and, under the "Initial View" tab, you can set a desired page view and page magnification. If you are using Acrobat Pro you can make and use an Action to do this to many PDFs in one go.
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If you are using Adobe Reader you can open the application's Preferences and for the Page Display category you can configure a desired "default". Note that a PDF that has a specific Initial View configuration set by the author will override the application default.
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Be well...