Is it possible to display a pdf-file in an R/3 screen?    

Displaying pdf files is possible if you use an html file that contains the pdf (use the View-command for the html file). You could also use the command  View "...myfile.pdf" (no screen coordinates), but in this case the pdf file is displayed outside the R/3 screen. You can also use the command  Image .... "Start=...myfile.pdf" which displays the pdf file when the user clicks on the image.