Oops, try that link again, I think I fixed it.
There is that MicroSD card option, but there's also some flash memory in the PAC itself, see this form (1646), also with lovely illustrations. To write to the MicroSD card, you'd just use the file and ftp comm handle commands (with the appropriate subdirectory and 8.3 file name limitations).
To save a file on the PAC itself to the on-board Flash "User File Storage" area (in yellow in the lovely illustration mentioned above), you can use the PAC Control "Control Engine" command called "Save Files to Permanent Storage". Neat-o.