Based on Balkan Bulgarian Airlines Boeing 737-53A LZ-BOB Serial #: 24921
To install simply open the .ZIP file, extract the .ptp file of the livery to a folder or desktop of your choice, open the PMDG Operations Centre, Aircraft and Liveries tab on the top, livery utilities and then "Install from PTP file".
Feedback and donations are always appreciated
Sachko767
Congrats !
(And nazdrawe to all the bulgarian folks here!)