About .pnm graphic file:

The portable pixmap format is a lowest common denominator color image file format.

24-bit color image that is formatted in text format. Each pixel is assigned a number from 0 to 65536 that defines the color of the pixel. Other information included in a PPM file includes the image height and width, whitespace data, and the maximum color value.

Because the PPM format is uncompressed and is inefficient compared to other image formats, it is seldomly used for saving large image files.

Help how to open PPM files:

Use graphic viewer or editor (XnView, Adobe Photoshop).

How to convert file with extension PPM:

Use Adobe Photoshop or ACDSee.