“At this point, I'd like to take a moment to speak to you about the Adobe PSD format. PSD is not a good format. PSD is not even a bad format. Calling it such would be an insult to other bad formats, such as PCX or JPEG. No, PSD is an abysmal format.”

(Followed by the real rant)

I’m not sure it’s worse than PDF, though. PDF started life as a text-based postscript replacement that made it possible to index into postscript files, allowing one, for example, to render page 214 of a file without rendering the previous 213.

When files grew too large, they added compression. Initially, that was base-85 (https://en.wikipedia.org/wiki/Ascii85), keeping the file text-based, but other compressors were added so that, now, the file is binary. They kept the index and all metadata in uncompressed ascii, though.

Then, they layered zillions of different features (3D graphics, forms, JavaScript, font embedding, etc) on top of it.