Re: Word 2013 alters date
The date in that document is a form field, of the type date, that's set to update to currentdate().
See this Office Help Page: https://support.office.com/en-us/article/Insert-edit-and-view-fields-in-Word-c429bbb0-8669-48a7-bd24-bab6ba6b06bb
If you want to view fields in any document ALT+F9 makes them visible. You can either choose to remove the field and put in the date you'd like to keep in the document, or you can use the CTRL+F11 shortcut in the field to lock it after you know it contains the date you want. For myself, I just nuke the date field and put in the text for the date as it should remain forever.
Form fields are great for saving effort every time something is opened, but if the document is to be then a permanent record, it's better to do a Select all (CTRL+A) then use the CTRL+SHIFT+F9 command to unlink all the fields and retain their current values. See: https://word.tips.net/T001864_Deleting_All_Fields.html
Brian - Windows 10 Home, 64-Bit, Version 1809, Build 17763
Explanations exist; they have existed for all time; there is always a well-known solution to every human problem — neat, plausible, and wrong.
~ H.L. Mencken, AKA The Sage of Baltimore