It appears so. If you upload your paper on RG and then choose it (as if you wanted to download it), and you'll see the choice "Generate a DOI for this publication".
Dear Sir, Thank you for your remark. It works only for conference papers, not for journal articles. I want to know whether our published articles (which have not been assigned a DOI by the journals) can be assigned new DOI by our ourselves (in ResearchGate or in any other way).