I have a PDF that is set to open to a specific page. In Adobe Acrobat Pro DC (version 2018.009.20050), I go to File -> Properties, Initial View tab. I go to the text box for "Opens to page." I try to remove the page setting in that box. The system will not let me; when I click OK it gives me an error message, "The page number cannot be left blank."
In other PDF's that I have, the page number IS blank, and the file opens at the last page viewed.
The kicker is that I read these documents on an iPad Pro; the Adobe Acrobat reader for iPad does not have the ability to set the reader preferences to "last page viewed." However, PDF's that have the "Open to page" setting as blank do open to the last page viewed.
How can I fix this PDF so that it will open to the last page viewed when I read it on the iPad?