Hi guys, thanks for bug reporting. :)
@ noo-b:
PDF creation is not yet admin configurable but will be soon.
For now you will have to copy your logo image file in:
"yourxoopsroot/Frameworks/tcpdf/images"
Then you need to change your makepdf.php file in yourxoopsroot/modules/xnews/makepdf.php file where from line 147 you will find:
 // set default header data 
$pdf->SetHeaderData(PDF_HEADER_LOGO, PDF_HEADER_LOGO_WIDTH, PDF_HEADER_TITLE, PDF_HEADER_STRING);  
//$pdf->SetHeaderData('', '', $firstLine, $secondLine); 
//$pdf->SetHeaderData('logo_example.png', '25', $firstLine, $secondLine);  
comment out line 148 and add somthing like:
 // set default header data 
//$pdf->SetHeaderData(PDF_HEADER_LOGO, PDF_HEADER_LOGO_WIDTH, PDF_HEADER_TITLE, PDF_HEADER_STRING); 
//$pdf->SetHeaderData('', '', $firstLine, $secondLine); 
//$pdf->SetHeaderData('logo_example.png', '25', $firstLine, $secondLine); 
$firstLine = 'Your Site Name'; 
$secondLine = 'Any thing you feel writing here'; 
$pdf->SetHeaderData('your_logo_file.png', '25', $firstLine, $secondLine);  
You can leave $firstLine and $secondLine empty if you want logo only to appear... Logo can be png gif...