// pdf to set of images convert -quality 100 -density 300x300 multipage.pdf single%d.jpg
// set of images to pdf convert -density 200x200 -quality 60 -compress jpeg form-.jpg form.pdf convert page.png mydoc.pdf
-compress jpeg -quality 90 -resize 1240x1753 -extent 1240x1753 // -extent actually extends the image to be 1240x1753, // while -resize keeps the image's ratio, fitting it into either 1240x... or ...x1753.
-gravity center // The -gravity parameter is optional but can be used to center the image when extending.