conversion of CBR/CBZ to PDF : output is not normal format

hello,

when I use Calibre to convert these files (CBR/CBZ) they generate a pdf which is "cropped". is does not come a normal A4 format. the width seems normal but the height is compressed and does not take the whole page. I can read the text and see the images but it is distorted.
what can I do about it. Is it linked to my parametrisation or is a general problem (I don't find any litterature on this on internet).

thanks,