Unable to save PDFs

When opening certain PDF files using the in browser PDF viewer (Adobe engine) the save button is greyed out, also it tends to be when this message is displayed "This document is digitally signed. Some signatures couldn't be verified."

Windows 11, Edge 128.0.2739.42, works fine in Chrome 

Example document link, https://assets.publishing.service.gov.uk/media/60b74244e90e0732b2acacb6/PA15_0421_save.pdf 

Any ideas?