A hand.

He started carving. The IDX3 format, he recalled from a long-dead forum post, was a proprietary pointer system for a forgotten CAD program called ArchiVector . The software died with the dot-com bubble. The trick, the post said, wasn't to open the index—it was to interpret it. The index didn't contain the blueprint; it contained the paths to the blueprint fragments scattered across the dead drive’s residual magnetic whispers.

A delicate, impossibly detailed sketch of a human hand, holding a single blue feather. The layers were annotated: tendon_map.vector , ligament_tension.curve , feather_barb.contour . But the bottom layer, the foundation layer, was named: for_elena_1997 .

You can use tools like Subtitle Edit to convert an IDX/SUB pair into an .srt (text-based) file, which is more widely supported by smart TVs.

If you are digging through old backups, you might find .idx files used by Outlook Express to organize mail folders.