Ensure that these tooltip-only Annotations are handled as "internalLink"s, to ensure that they behave as expected in PresentationMode (e.g. they should still use a `pointer`-cursor).
Ensure that `PDFLinkService.getDestinationHash` won't create links with empty hashes, since those don't really make a lot of sense in general (this improves things for tooltip-only Annotations).
This PDF file can be used for testing: http://mirrors.ctan.org/macros/latex/contrib/pdfcomment/doc/pdfcomment.pdf#page=14