You could create a custom event on the purchase_requisition_tab table.  Then use the Purchase_Requisition_RPI to create the data needed for the report.  Then if my memory is correct, there is a method call in Report_sys for creating the PDF from the data.

Thanks, I tried capturing the SQL that is sent to the server in the console window when a Requisition is printed but it doesn’t really give me what I want. This is the link I got the code from that enabled me to create a Purchase Order pdf manually, it would be great if I could find something similar for Purchase Requisition. 

Actually I think I can do it now. I found this link which shows how to do it for a Shop Order Work In Progress report and I was able to adjust it to do it for a Purchase Requisition (see code below link). When I run it, it creates a print job

https://gist.github.com/damithsj/70fccd01d46a7ac6de60a4f587ef1b20

DECLARE

   report_id_         VARCHAR2(100) := 'PURCHASE_REQUISITION_REP'; -- Report ID
   report_attr_       VARCHAR2(2000) ; 
   parameter_attr_    VARCHAR2(2000);
   distribution_list_ VARCHAR2(2000):= '';

   result_key_        NUMBER;
   printer_id_        VARCHAR2(100);

   print_job_attr_    VARCHAR2(2000);   
   job_contents_attr_ VARCHAR2(2000);
   print_job_id_      NUMBER;
   instance_attr_     VARCHAR2(32000);
   lang_code_         VARCHAR2(2);
   printer_id_list_ VARCHAR2(32000);

BEGIN

  ------------------------------------------------------
  -- (1) Create Archive instance
  ------------------------------------------------------

  -- Create the report attr
  CLIENT_SYS.Add_To_Attr('REPORT_ID', report_id_, report_attr_);

  -- Add report parameters
  CLIENT_SYS.Add_To_Attr('REQUISITION_NO', '312969' , parameter_attr_);


  -- Create Archive instance.
  -- It will return the result key
  Archive_API.New_Instance(result_key_, report_attr_, parameter_attr_);

  ------------------------------------------------------
  -- (2) Create Print Job and contents
  ------------------------------------------------------
  -- Get the user default printer.
  printer_id_ := Printer_Connection_API.Get_Default_Printer(Fnd_Session_API.Get_Fnd_User, report_id_);
  Client_SYS.Add_To_Attr('PRINTER_ID', printer_id_, print_job_attr_);

  -- Create Print job  
  Print_Job_API.New(print_job_id_, print_job_attr_);

  Client_SYS.Add_To_Attr('RESULT_KEY', result_key_, job_contents_attr_);
  Client_SYS.Add_To_Attr('PRINT_JOB_ID',print_job_id_,job_contents_attr_);
  PRINT_JOB_CONTENTS_API.New_Instance(job_contents_attr_);

  ------------------------------------------------------
  -- (3) Print!
  ------------------------------------------------------  
  Print_Job_API.Print(print_job_id_);
commit;
END;

I am not sure what the cloud version is like, but IFS 10 requires more values sent to Print_Job_API.New.

      Error_SYS.Check_Not_Null(lu_name_, 'PRINT_JOB_ID', newrec_.print_job_id);
      Error_SYS.Check_Not_Null(lu_name_, 'STATUS', newrec_.status);
      Error_SYS.Check_Not_Null(lu_name_, 'EXPIRE_DATE', newrec_.expire_date);
      Error_SYS.Check_Not_Null(lu_name_, 'USER_NAME', newrec_.user_name);
      Error_SYS.Check_Not_Null(lu_name_, 'PRINT_JOB_OWNER', newrec_.print_job_owner); 

Thanks for your reply, the code I posted is doing what I require though.