Convert pdb to pgm

What is the difference between .pdb and .pgm?

Description: Standard data format used by several different programs on Palm-based PDA devices; may store various types of data, such as eBooks, word processing documents, spreadsheets, databases, maps, and image files.; A PGM file is a grayscale image file saved in the portable gray map (PGM) format and encoded with one or two bytes (8 or 16 bits) per pixel. It contains header information and a grid of numbers that represent different shades of gray from black (0) to white (up to 65,536). PGM files are typically stored in ASCII text format, but also have a binary representation.