that if this .sig file extension is used exclusively by the software developers who created your invitation card creator software, then there is unlikely to be any conversion software available.
You didn't say what software you are using, but the File Extension guide here; http://filext.com/ lists only one use of the .sig file extension by Broderbund.
Such software is normally only used to 'print' invitation cards. Those cards are then sent out, (postal), or given by hand, and not through emails.
Hi I have a software program for creating invitation cards etc. When I save it the extention is .sig. This is a problem because when I send it in an email no one can open it. So I believe I need a file coverter software program? I have no idea which one to use. Im using xp. Hope someone can help. Thanks