PDF is a file format developed by Adobe Systems for representing documents in a manner that is separate from the original operating system, application or hardware from where it was originally created. A PDF file can be any length, contain any number of fonts and images and is designed to enable the creation and transfer of printer-ready output.
Each PDF file encapsulates a complete description of a 2D document (and, with the advent of Acrobat 3D, embedded 3D documents) that includes the text, fonts, images and 2D vector graphics that compose the document. They do not encode information that is specific to the application software, hardware, or operating system used to create or view the document.
The .pdb file extension is a database format used for the Palm OS platform. The PalmDOC eBook file type is a version of the PDB format. The proliferation of eBooks has left this format behind due to the lack of support for DRM protection meaning only royalty free text is typically available.
The format supports reflowable content however the format lacks some of the features found in more modern eBook formats, for example only providing a very basic contents table. The format features RLE compression which was crucial because the format was designed for the low storage capacity Palm devices of the 1990s.