If I understand you correctly: I simply cannot call the FPDF function from a page which has already outputted HTML, and the list.php page immediately outputs HTML when it opens.
Now my dilemma is: how can I let the user print a report of the list? I need the "Print Report" button to appear on the list.php page.
Why are you insisting on using the same file for two different things? The simplest thing is to create a new file that generates the PDF (and does nothing else) and have the form direct to that file. You are just making it more complicated than it needs to be.