How to open an .tn3 file on Windows 10 HP laptop computer?

Solution 1:

A TN3 file is from Atari computers

TN3 file

A TN3 file is a bitmap image used by Atari ST computers, which Atari released in the late 1980s and early 1990s. It contains an RLE-compressed image that may or may not be animated. If the image is animated, the TNE3 file contains multiple bitmap frames and the animation sequence's speed and duration

The TN3 format is one of several Tiny image formats used by Atari ST computers. Tiny images are also stored in low-resolution (.TN1 files) and medium-resolution (.TN2 files) formats. They may also be saved with the .TNY extension.

If you need to open a TN3 file, a HEX editor would be your best bet. Lots of HEX editors around. I use Ultra Edit.