i have a processing sketch in which i work with several images and their transparency. when pressing 'S' i want to save the current screen to a pdf using this code:

void doPDF()
{
 beginRecord(PDF,"myfile.pdf");
 background(0)
 endRecord();
}

i just get a black screen saved as pdf without the images i see in my applet?
is there any  trouble using images and saving them to a pdf?
i tried to use the same script and just drew circles to my screen and then used the save-to-pdf-function. that worked quite well. so i came to the point that there must be trouble with images (png - files) and the pdf.

i'm glad for any help

Well, your code snippet just writes a black screen (the background(0) instruction) to PDF, so you get what you put there.

Did you looked at the reference page pointed out above?
To summarize, you need to call beginRecord() when pressing S, setting up a flag telling your started to record.
Next call on draw() will draw on screen and in the PDF file, and at the end of draw(), call, if the flag is set, endRecord() and reset the flag.

I might try and do a bit of code to illustrate this better if you need, I haven't tried this library yet.