The wordpress pdf plugin supports unicode UTF-8. The problem is not the plugin, but the pdf24.org online converter. gujarati is an unusal language and we do not have fonts for that language installed.
Ok, this could be because our PDF converter has not every special language installed. We support many languages, but not all. I think that we can't comply with your desire in the near future.
as of today: the PDF24 WordPress plugin ("PDF24 Article To PDF") has been discontinued and is no longer maintained.
To create a PDF of a page in Gujarati (or any other language) today:
Open the page in your browser and print it to the PDF24 printer of PDF24 Creator (free for Windows: https://tools.pdf24.org/en/creator). The PDF is created on your PC with the fonts your browser uses to display the page.