With the recent versions a lot of PDF stuff has been added.
But I cannot read anything about the license needed to create/edit PDF files. Does this mean Xojo Inc provides the tools, but not the license for using them in your app?
Knowing Adobe, releasing an app that can edit PDF files and not having a licence can get you into serious trouble.
PDFDocument is a class to create PDF documents from your Xojo apps. Not to open/editing existing ones (a different beast 
) yet…
What license is missing?
When you build in Xojo and you paid for the Xojo license, that covers all use of their frameworks within your applications, so you are covered.
if you use other PDF things like MBS Xojo DynaPDF Plugin or Einhugur PDF Plugin, you would need to pay for that. But there is nothing to pay to Adobe.
PDF is an Open Standard, that’s means you can implement it as you want freely.
From : PDF - Wikipedia
" Anyone may create applications that can read and write PDF files without having to pay royalties to Adobe Systems ; Adobe holds patents to PDF, but licenses them for royalty-free use in developing software complying with its PDF specification."
In case this vanishes from the web:
This “waiving of licensing” terms was before they declaring “now it’s an Open Standard, use it as you wish”.
Have in mind that if you implement some parts using OTHERS technologies patents, you should license those technologies, as RC4. If you implement RC4 encoding, for example, you should license it.
There’s always ARC for that…
Anyway, returning to the original post… I think it is replied already with my answer. In summary: PDFDocument (still) doesn’t open/parse/edit PDF documents. Just creates them 
RC4 = ARC4
There’s AES nowadays.
No worries, creation, editions, etc are free too, what Adobe charges is using THEIR SDK with their libs, not licensing the technology, but the use of their libraries. Anyone is free to create their own based on the standard.
As we do
Yeah… but I can assure you that ARC is needed in PDF for some things
I guess optional things.
Nop “optional” but “required” in the implementation of some PDF features (following the PDF Standard book) 
I know a GIS software that implemented just AES, and Python (I don’t know why) implemented just RC4, so both down talk to each other unless the PDFs are open.
