@SH-1616 ,
To answer your questions:
- If you want to share documents externally, it's necessary to publish your RMS into internet, in this case we could setup reverse proxy in a new server, for more details, please refer to http://ramch011.blogspot.com/2015/06/configuring-rms-in-sharepoint-2013-on.html
- To use PDF files in libraries that the owner has protected with IRM, the user will need to obtain one of the following PDF-compatible readers(such as Foxit Reader or NitroPDF). https://learn.microsoft.com/en-us/microsoft-365/compliance/sp-compatible-pdf-readers-for-irm?view=o365-worldwide
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