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Spore encoded the creature data in the alpha channel... which always struck me as odd since they managed the site that hosted the images and could guarantee metadata wasn't removed after upload. I think a few other games used metadata to share but the names aren't coming to mind.

Back in the day I think Macromedia Fireworks used this model as well..

LibreOffice can embed the source document when exporting to PDF. They call this feature Hybrid PDF.

draw.io / diagrams.net also embeds the data inside PDF.

It's possible to export LaTeX to PDF with the latter containing the LaTeX source.

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