Go with the arrows to the desired class name and press Enter.
Currently there is no way to generate a sequence diagram from a communication diagram, or vice versa.
Communication diagram is kind of Interaction Diagram and reuses some UML elements from Sequence Diagram, but is very limited. Most of advanced Sequence Diagram elements can't be reflected in Communication Diagram. It includes all kinds of CombinedFragments, Gates, Nested activations, Sequence of messages and more, so even theoretically Communication Diagram can't be equal to Sequence Diagram.
Currently we try to gather information what would be the benefits of this feature. We would be very grateful if you could share your opinion with us.
For non automatic elements reuse - Communication Diagram can be generated inside the same Interaction (as Sequence Diagram). In this case Lifelines can be reused by simply drag'n'drop them from Interaction directly to communication diagram.
It is not recommended to use the following fonts for diagram saving as .eps, .emf, and .wmf:
Default, Dialog, DialogInput, Monospaced, SansSerif, and Serif.
This is a know problem of Mac Word. Still we don't know when it will be fixed.
Such problem really exists and will be fixed in future releases.
As a workaround we suggest to save your diagrams as SVG and then use free Inkscape editor (http://www.inkscape.org/) to export diagrams as hi-res png.