Built-in File Formats
Where can I get the file formats for the built in apps?
There are couple of ways to find this information. The current Palm OS SDK has source code to all the built-in apps, from which you can extract the necessary info. This gives you the structure of the records as far as the Palm-side app is concerned. Palm also has a publication called "Palm File Format Specification" which you can download in PDF or HTML format, or you can buy a printed copy.
The format of the PRC files is described here.
There's also a good explanation of the formats at Oingo's Palm programming directory. This includes both info on the PDB file format, as well as inside info on the format of the records within the PDB file. There are descriptions for records used by the memo pad, to-do list, address book and date book apps.
Adam Tow's iKnapsack system may be helpful to you if you need to convert Internet-based content to a Palm database.
Note that if you want to read/write the PDB files on the PC side in the Palm backup directory, you'll have to take into account the fact that Palm Desktop and Hot Synch both modify these files. If either is running, you can't be completely sure that you can safely modify the files.