Share point custom workflow

Question

Hi all,

I have a requirement that,
 
once the document is added to document library the the custom approvalworkflow will get triggerd and the docuement moves for reviewer review 
once the review is done, the document should get convert to PDF format and the workflow should proceed till end.

Issue that i am facing is once the docuement is converted to PDF it is new document all together and  one more item in the document library
so in this situation what is the best way that workflow should continue for the PDF docuement instead of word document.

please reply on this asap waiting for the reply

Chetan