I have an existing web page that I want to remove from public view but don't want to delete the page.

 

Go to the page list and uncheck the "Visible in Navigation" checkbox found towards the bottom of the right column (shown in yellow below). Don't forget to click the "Update" button to complete the action:

 

 

This checkbox removes the link to this page from the menu of the website but does not prevent someone from accessing the page from an old bookmark of the page.  If the page is a manually published page, you can click the "UnPublish" button.  An unpublished page is not only removed from the menu links but it can not be viewed even with an old bookmark to the page.