Convert app to dds Online: app2dds

You can use Tom's Editor to easily convert images from
APP .APP to Direct Show Surface .DDS.
Tom's Editor is a free, online image manipulation and converter program.

Go to Tom's Editor

APP

APP is an image format with extension APP.

DDS

DDS are files invented by Microsoft to be used in games, mostly as textures. Images can be compressed to save space but the compression methods defined by DDS are all very fast in terms of coding and decoding.