I don't know that this is really feasible automaticaly under LiveCycle ES. While its true that Forms can be rendered as either PDF, HTML or as a Form Guide - the designer for Form Guides is different to the PDF and HTML designer. You cannot take a form designed to be rendered as PDF and have it automatically render as a Form Guide.
In some of the Adobe LC ES demo's they show forms that are displayed as Form Guides - then they have a button to redisplay as a PDF. In these examples someone has used the Form Guide designer to create the Form Guide. Then they have used the PDF Form designer to create another Form Design to render the PDF view. Both designs would share a commom XML data model.
So.. You are saying that XDP can be rendered as PDF, HTML or Form Guide. I kind of knew that already. And I have made few Form guides with Guide Builder. But I still didn't get full picture about this. So we first create a XDP and after that, we create a Form guide with Guide Builder. Done that.
What after that? I must choose some render service in process designer but if I want user to be able to switch between form guide and pdf in runtime, how I can "enable" this? For example, I want the user to fill the data with form guide but the user could switch to pdf at some point to print the form and switch back to form guide to submit it. How actually do this?
If you use the Sample - Forms/Render Form Guide/Render Form Guide service as your render service to render your form into a guide, you should get 4 icons in the top right of your guide. The last one allows you to switch between PDF and Guide. The other one allow you to print, email and save the PDF version of the guide.
If you're making your own service, make sure the "Guide PDF" option is set to true on the renderFormGuide operation