Convert pgm to fits

What is the difference between .pgm and .fits?

Description: 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.; The Flexible Image Transport System (FITS) file format is a digital file format used primarily in astronomy for storing, transmitting, and analyzing scientific images and data. Developed in the late 1970s, FITS was designed to provide a standard for the interchange of astronomical data, facilitating the sharing and analysis of data among astronomers and researchers worldwide.