What is expected when submitting to a conference
It is typical to just provide a title and abstract.  In my experience, they are usually submitted in plain text or TeX format, not even in pdf.  You are never asked to provide a paper, though for some conferences you may be asked for notes later.  Based on your question, I guess the organizers want you to submit a file that they will just link to on the webpage for an abstract, which could be a pdf or plain text.  If you're still uncertain about what to do, just ask the organizers what they prefer.