Generally, any file with a defined pixel size will allow 100% zoom (1 to 1-pixel mapping on screen) using the original file.
This is true for most image file formats. It is also worth noting that using this feature has a significant performance impact on the FotoWeb server. This is also the case for RAW files.
For file formats that don't have a real pixel size but where a preview can still be generated (such as documents and presentations), a preview can be created but not zoomed. For instance, Word and PowerPoint documents and PDFs can be previewed and leafed through but not zoomed in.
Videos do not support zooming. The same is the case for all file types for which no preview can be created.