How to Merge Contacts in Outlook

Query about how to merge contacts in Outlook nowadays become much more frequent due to its various usage. Users have huge demand to synchronize the contacts to your phone and devices but it is quite typical if you have multiple PST files. Thus, after knowing how to merge contacts in Outlook 2010, 2007, 2003 etc. gather all the contacts in Outlook address books from multiple PST files into one file.