Convert dng to pnm Online: dng2pnm

You can use Tom's Editor to easily convert images from
Digital Negative .DNG to Portable aNy Map .PNM.
Tom's Editor is a free, online image manipulation and converter program.

Go to Tom's Editor

DNG

Digital Negative is an image format with extension DNG.

PNM

PNM images are uncompressed 24 bit RGB images. Can cannot store Alpha channel. PNM images come in 2 types: binary and text. Especially popular on Linux.