The pdb file extension is a file type which is used for storing data intended for devices that use the Palm OS, which is an operating system for hand-held devices. There is a specialized version of the format, called PalmDOC, which is used for reading ebooks. It is also compatible with the GarnetOS, and the open source Access Linux Platform, which are also used for mobile devices.
If you want to open a file with the pdb file extension on your PC, do a google search for Open Office. Open Office is a series of programs, similar to Microsoft Office, that can be used to create and access many different file types including written documents, spreadsheets, and presentations. It is available for free and it is open source, meaning that the code used to create the program is available to anyone and it is created written transparently.
Once you have downloaded and installed Open Office, simply right-click on the document with the pdb file extension, choose “Open With” in the drop-down menu, and select Open Office from the available options. You will then be able to view and edit these types of files on your PC as well as your mobile device.