The fancytooltips package:

The package was inspired by the cooltooltips package. In contrast to
cooltooltips, fancytooltips allows inclusion of tooltips which contain
arbitrary TeX material or a series of TeX materials (aminated graphics) from
an external PDF file. The links and JavaScripts are inserted using eforms
package from the AcroTeX bundle. Similar packages are cooltooltips,
pdfcomment, ocgtools and AcroTeX. The PDF file must be opened in (free)
Adobe Reader.

Possible applications include automatical extraction of equations,
definitions, theorems and other stuff from the document and inserting
previews to \ref, \cite and \eqref commands.

Supported by grants 18/2006, 99/2008 and 131/2010 of Higher Education
Development Fund (FRVS).