Yes, they are really that complex. The Office file formats are incredibly complex. Lots of moving parts, many different ways to express the same thing, lots of

Yes, they are really that complex. The Office file formats are incredibly complex. Lots of moving parts, many different ways to express the same thing, lots of legacy stuff, endless obscure low-level bit shuffling. The OLE container is a small filesystem. The Word format includes its own heap. What makes them fast is that they were designed to not require parsing at all. They are essentially a memory dump and can be loaded with a simple mmap. But if you want to "understand" what that data means, then you have a long and complex road ahead of you.