Specialized utilities for Symbian phones like the SIS to JAR Converter can be used to convert various Symbian app installation packages (.sis, .sisx, .jar) between each other so they can be used on different versions of Symbian. However, .jad files are just app descriptors and do not contain the actual app, they may be generated alongside the .jar file, but unlikely directly from a .sis file.
Convert Symbian installation file to Java application descriptor file.
We found one software available in the database for this conversion.
Microsoft Windows software - convert sis to jad on Windows
A dedicated converter for Symbian packages
Convert from sis file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.