ProCite
From Just Solve the File Format Problem
ProCite is a reference management software program originally developed by Personal Bibliographic Software in 1983, it was discontinued in 2013 in favor of the software title EndNote currenty owned by Clarivate.
File Identification
ProCite versions 1-4 used a database system of files with extensions, .DAT, .PMT, .REC, .SRT.
ProCite versions 5+ used database extensions, .PDT and index file .PDX. Along with Output Styles .POS, Term Lists/Journal Lists .PJL, and Workforms .PWF.
.PDT files begin with hex values "B4 F4 5C 00 0C C1 9A 00
"
ProCite .PDT files can be opened with Endnote X1 and saved as EndNote .ENL file.