How can I fax a document generated by RS Documents, Conga, or other document generation app?

You need to configure the app to generate a PDF with a specific filename and attach it to the record. The filename could start with the word “Fax-” for example. Then configure Opero Fax to auto send the pdf that gets attached under Opero Fax Configuration in Field settings to look for a pdf with a filename that starts with the word “Fax-“.