PDB format is file type developed for PalmOS. Its whole name is Palm Database and its extension is .pdb. His main advantages are many. He saves lots of information, for example latest time of editing, date of creation or its speed. The main advantage is save of RAM memory in devices where the files are viewed. One of the best known viewers of this format is Aports Reader, which is unfortunately not updated for a long time.
As we write above, it has many viewers. The best known is Aportis Reader, which can´t be downloaded. Format on its own was developed in 1996 by Rick Bram, when he was trying to compress size of text files in Palm OS. In the same year was developed Palm Doc format, which was later on bought by Aporties Technologies Corporation who renamed it to Aportis Doc. Since 2002 was this program stopped and it is no more used.
The best known other programs for viewing files saved in this format are DeepReader (no more updated), Palm PDF (freeware) or LionDoc. Moreover there are plenty of applications able to read these files.