The sis file extension is used for one of the file types used in Apache. The contents of any file with a .asis extension will then be sent by Apache to the client with almost no changes.
How to open:
The asis files are used for internal purposes of Apache http server.
How to convert:
As far as we know, this .asis file type can't be converted to any other file format. This is usually the case of system, configuration, temporary, or data files containing data exclusive to only one software and used for its own purposes. Also some proprietary or closed file formats cannot be converted to more common file types in order to protect the intellectual property of the developer, which is for example the case of some DRM-protected multimedia files.