A global list customizer which adds functionality to all document libraries in SharePoint Online to convert one or more documents in-place to PDF, or download one or more documents as a PDF. When selecting multiple documents for download they will be downloaded as a zip file. The converter uses built in API’s of converting to PDF.
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Source: https://github.com/pnp/sp-dev-fx-extensions/tree/main/samples/react-command-convert-to-pdf