Although it was effectively the case before, since 2008 PDF is an open format. It's quite misleading to compare it to a binary for which source is unavailable. Since the format specifies compression, not every part of a PDF file may be easily observed in a text editor, but there's a bunch of open software that can read (and edit, and produce) PDF.

Producing and reading PDF isn't the issue.

Again, we have open source tools that will generate, mangle, introspect, disassemble, etc. to both ELF and PE binaries.

What PDF is not is the "preferred format for development", no matter how good the open-source tooling is.

Sometimes practical considerations preclude using the most "preferred format". Will editing this white paper really be a significant obstacle to deploying a system like the one it describes? Conversely, does anyone ever release a white paper in LaTeX only?

What are you on about?

No one here is saying that an open-source project to assist with Hyperloop could not be launched. Nor that the ability to edit the whitepaper that was released has anything to do with this proposed open-source project. Nor even that people typically release whitepapers only in LaTeX format.

However if an open source project will be launched with Hyperloop then its success will be at least somewhat dependent on the ability of participants to meaningfully contribute.

If "contribute" just means discussing key points then a simple Wiki might suffice. However if "contribute" means technical designs, then the actual drawings and data will be what's needed, not glorified screenshots of AutoCAD and MATLAB.