What is required to export a requirements specifications documents from the "Author documents viewset" in Integrity to a ReqIF format so other requirements programs can import?
Generally speaking, the Integrity Requirements Connector product is the way to export documents from Integrity into other systems such as IBM Doors. There is an IRC User Guide which you can review for some further details or you can open a case with PTC Technical Support if you have some more specific questions about that setup.
Can we export document from integrity and import to DOORS Next Generation ?
I'd suggest opening up a Support case with the IRC support team, to confirm if import into DoorsNG is supported or not. DoorsNG is supported, but I'm not sure which import/export functions are supported.