2. Suppose there is an existing spool, an OTF or SMART file, can I create/reprint it as PDF spool (As mentioned in the screenshot, a spool with the pdf icon, as a pdf spool).
I don't know enough to really advise, but would not even try it without ADS. From Administering XDC Files for SAP Device Types (Report RSPO0022):
When printing Interactive Forms, the complete form is sent to the Adobe Document Services in XML format. These services return “parts” for the forms. A part always consists of a PDF file and a print file (PostScript, PCL, or ZPL), which are placed in the Global Directory.
The "ADS spool" consists not just of PDfs (which is device independent format), but also of so called print files. The place where all the attempts to mimic ADS behaviour will IMO fail as unfeasible, is trying to manage XDC - a printer description in XML format the ADS requires to create the print files - and creating the print files itself.
cheers
Janis