John Brennan, the executive in charge of PDF, Flash, and other platform technologies at Adobe, has resigned to join Silver Lake, a private equirty firm that has previously hired away the likes of Michael Capellas from HP and Ed Zander from Sun.

Brennan, who was previously senior VP of Adobe's Platform Division, is now a managing director at Silver Lake Sumeru, a new business which will invest in medium-sized technology companies.

Brennan's departure from Adobe comes not long after the replacement of Bruce Chizen with Shantanu Narayen as Adobe's CEO in January.

After serving as senior VP for SMB operations at Hewlett-Packard, Brennan arrived at Adobe in 2004 as senior VP of corporate development. There, he spearheaded mergers and acquisitions that included the buyout of Macromedia in 2005.

Recently, Brennan was also in charge of Adobe AIR, a cross-OS application runtime, and Adobe Flex, an open source framework for Web development.

Following Chizen's exit from Adobe, Brennan stayed on at the company long enough to oversee the final releases of Flex 3 and AIR last month. There's no word yet as to who will assume Brennan's post.