Deleting the default margin?

Dears,
I have amazon kindle PW3, and i use it for PDF files, my steps to view the files in my device as below:

1- after downloading the file to my laptop, i edit the file by removing the white margin
2- change the file from PDF to JPEG
3- use KINDLE COMIC Converter
However, whenever i sent the file to my kindle, i cannot get rid of the default margin in my kindle, is there any way i can view the file without any margin?

thanks in advance.