[rahimnathwani]

"but there must be tremendous internal complexity in the PDF format for tiny changes to alter the whole structure."

Imagine a simple file format that doesn't support text wrapping, but allows you to specify elements as (x, y, s) where (x, y) specify a position, and s is a string that will be written left-to-right, truncated at the edge of the screen.

That's a simple file format, right?

But inserting a word somewhere early in that document would change the string within every element in the rest of the paragraph. And maybe move the y position of every element later in the document.

That would be a PITA to diff. Even more so if the document has more than one column.