First, this is a programming website, so you should identify a programming context. This question will probably be closed because it belongs on the soon to be launched serverfault.com
Note: I am unsure if other open source pdf editors provide this type of functionality.
That's weird you couldn't do it with Standard. I did test it with Professional and it worked, so I guess it only works with that. Sorry.
To set the default magnification, you need Adobe Acrobat Standard or Professional not Reader to have the ability to edit pdfs. Then when you open the document, click File | Properties. Click the Initial View tab and enter 72% in the magnification text box and click ok. Save your pdf and reopen it. It should default to 72% magnification when it is opened.
Tried the procedure with Acrobat Standard and unfortunately the magnification level did not get saved. When opening the file, the document automatically adjusts to the adobe reader window size. The reader seems to default to Fit to window on open even when it's unselected at save time.