Hi Mamta,
sub reports are exclusively available for rdd based reports. The primary reason for this is, that the xsd format does not cater for the concept.
As you intend to use sub reports as a means to reuse document fragments, you might want to consider injecting or replacing a part of one .4rp file with a part from another file via a script much like you would copy past a header from one report to another in the designer.
That way you could have a "master" design from which parts are copied into all dependent designs whenever the master design is changed.
Manipulating design files with scripts can cause runtime errors if it isn't done correctly. Correctness can be checked by loading and saving the file in the designer. If it didn't shake during the process, the patch it fine.
Best regards,
Alex