Help with iconv command

Hi ,

I am using iconv command to convert a file in UTF-16 format to UTF-8 format. This command will work for few files but for some showing an error as bad input character.
But if i copy the contents of the file for which it is showing "bad input character" to a new file and perform the conversion it is working.

Please let me know how this iconv command works.
And also any way by which this error can be resolved.

Thanks,
Shruthi