May I recommend .html in that case? You can embed scripts that control who can run it, having it fetch a decryption token from a server or require a decryption password with a safe password hashing algorithm of your choice

It's much more versatile than PDF and, if the algorithm decides the user is allowed to read the document, then the user gets to make use of all of the document's options like a better search function (PDF can't find words that are bro-

ken across lines because that information of what's a word is gone, transformed into coordinates of what characters need to go where). It's also much more readable on different screen sizes, as the user can resize the window to whatever is comfortable on a 27" screen, or fits on their pocket e-reader. You can even draw it on a canvas if you want to prevent people from extracting the decrypted strings (though it's evil, you have that option). There's only benefits!

PDF is the lazy way to half-ass a read-only document while screwing, ahem, making anyone using a mobile phone zoom, pan, and squint. Thankfully, phones are falling out of fash— wait, scratch that, I just heard text reflow is more relevant than ever as phone use continues to soar