In ArcGIS Hub, there is no preview and optional download for linked PDF content. Prior to the February 2024 release of ArcGIS Online, this was a possibility. On an ArcGIS hub site, any PDF added as content to a shared group before the release can be previewed. For any PDF files updated following the release, previews are no longer an option and the PDF automatically downloads upon selection on the documents page of the ArcGIS Hub site.