How Would be differentiate the latest version of any document over the older version?

Dear Samir,

Well, I've two answers for your single question. :)

1. If you are only concerned about how to know in the latest version of the same file located in multiple location of your PC/ external drive. Then you could get your file explorers help by viewing your specific documents date created, and date last modified. 
2. Standard word processors provide you with the option of document markup, through which you could track the changes being made to the document overtime by yourself or other users in the reviewing pane. 

Regards,

SAAA.

Given a document follow standard document

Date and revision number should reflect on it

Therefore tracing latest version from old is not an issue.

If date and revision number not exist

You have problem with documentation standard and its execution