Complex sentence: The history of Adobe began when Geschke and Warnock first met and start working together at Xerox PARC where they develop Interpress, a page description language that was kept proprietary.
Split into simpler sentences: The history of Adobe began when Geschke and Warnock first met and start working together at Xerox's Palo Alto Research Center (PARC). There, they helped develop Interpress, a page description language which Xerox kept proprietary.