SpreadUbuntu is restricted to several file formats. Those are:
Image: required to thumbnail, even for documents
Huge Image: optional and allows a wider variety
Source: strongly encouraged to allow derivatives and translations. Should be editable - especially text. Archives are encouraged, and should include as much source content as possible including fonts, background images, and even a license. We also encourage use of formats that are easily readable in Open Source programs.
SVG - re-sizable vector graphic. Editable in Inkscape
PDF - specialized for printing. Editable in Inkscape
PSD - Adobe Photoshop format, but editable in The GIMP