Convert Images to PDF with ImageMagick
The command
The following command will convert a series of image files into a PDF file that fit into A4 paper size.
$ convert a.png b.png -compress jpeg -resize 1240x1753 -units PixelsPerInch -density 150x150 multipage.pdf
References
- convert images to pdf: How to make PDF Pages same size - Unix & Linux Stack Exchange
- ISO 216 (International standard paper sizes) - Wikipedia