the guide It is not clear

Is it possible write down the necessary steps  ?

If you are using the workflow to get the form and all the forms fields are blank then what you need to do is make sure your URL calls the form in a way to load the data.

For instance assume your URL is http://whatever/runtime/form.aspx this will always bring up a blank form. If you create a paramter called ItemID and you pass this in the url so it becomes http://whatwever/runtime/formaspx?ItemID=X where X is the record ID of the data you want in the form.

You then need a form rule that says if paramer specified go get the data for the form. either a method call on the field or a smartobject call that maps the data.

Make sure your form works with the URL outside of the workflow. You would use a field to store the ItemID for the URL now when you produce the PDF it will have data. the inout propery for the control is where you use the URL you built. Also a reminder that the workflow runs as the K2 service account so it needs to have access to wherever the data is stored.

I hope this helps.

Another way to accumplish this requirement is to create an SSRS report. By calling the SSRS SMO you can export without even opening up the report. This allows export to a variety of formats.

This will also give you greater flexibility to format the excel export into a more meaningfull format.