This information about how to link an image to a word document is really useful, thank you. Anyway, it was not exactly what I wanted. Vector images are good to represent math graphics because you obtain perfect quality. And they dont need much space to store the image (in fact they dont need almos any HD space..).

Anyway, today I have found the solution to my problem. Reading the Matlab help i have found this:

"EMF Files: (Enhanced MetaFile)

Enhanced Metafiles (EMF) are vector files similar in nature to Encapsulated PostScript (EPS), capable of producing near publication-quality graphics. EMF is an excellent format to use if you plan to import your image into a Microsoft application and want the flexibility to edit and resize your image once it has been imported. It is the only supported MATLAB vector format you can edit from within a Microsoft application. (Your editing ability is limited. For the best results, do all your editing in Microsoft.)

A drawback of using EMF files is that they are generally only supported by Windows based applications."

Matlab also highly recommends the use of EPS files. In fact, it seems that excluding Vector Image Editors specific image formats (such as ".AI" for Illustrator), the best options are to chose either EPS (goor in general), either EMF format (only for microsoft apps).

Thank you again,

Jesús