I,m looking for a solution to trigger an action on Openhab with the use of an external NFC reader - (Just like the function on the Android App).
Anyone have any suggestion I’ll be happy 
external to what server & os? OpenHAB is cross platform.
With an External reader I mean one that’s NOT attached to af phone running Openhab client (Android).
I want to send the UID of a particular NFC tag to Openhab and process that UID to trigger Action/Rules.
I assumed you meant external to your OpenHAB server. see why we needed more detail?
Well I wrote like the Android App - so I thought it was obvious
LIkely if you are connecting an NFC Reader to ypur phone it would depend on the OS version & tne manufacturer’s customizations 
I would like to achieve this without a phone - a NFC desktop reader USB or RS232, and transmit the UID to openhab - I don’t need the payload of the nfc chip.
Have you looked to see if it can be done with an esp8266 with some sort of reader?
Decided to go with a Rs232 reader, connecting that to a TCP/IP - Serial gateway and using the Serial binding.
Hopefully this will work