Direct Access Archive, or DAA, is a proprietary file format developed by powerISO for disk image files. And it is very simple to convert to ISO in linux. You just need an utility called daa2iso.
Install it on a RPM based system using 'sudo yum -y install daa2iso' or on a debian based system using 'sudo apt-get install daa2iso' . And to use the utility, just type the following:
terminal: daa2iso source-file.daa dest-file.iso