If only a raster image is open, this will be saved as a PDF file.

 If only a vector image is open, this will be saved as a PDF file.

 If both a raster and a vector image are open, both will be saved as a PDF file.

You can also save a file as PDF using File Menu > Raster > Save As.

This will save the raster image as a PDF file. If a vector image is open, the vector image will NOT be saved in the PDF file.

You can also save a file as PDF using File Menu > Vector > Save As.

This will save the vector image as a PDF file. If a raster image is open, the raster image will NOT be saved in the PDF file.