Try changing the PARAMETER type from 'String' to 'Object' and repeat your test - same issue ?
Additionally - the TRACER screen you show; appears (maybe) to show you DO have the raw bytes of the file (it starts with 'PK' - suggesting it is a ZIP (rather than a PDF ?) though ? ) - but the TRACER itself is unable to display the BINARY file ? (OR: it could mean a Byte->String Cast has already corrupted the RAW string).
Try changing the PARAMETER type from 'String' to 'Object' and repeat your test - same issue ? - yes same
The file which i am trying to download is a docx file , file name and path is set in the step 2 of the activity , document path and name is correct as i can download when i hit the url directly in the browser (this url is restricted to client network , will not work in public domain)