Hi emonshr,
I do quite a bit with asciidoctor-pdf, which I believe your question is about.
To define your own style (font, size, page margins, header, footer, etc), you should create a custom theme file in YAML. Asciidoctor-pdf comes with a theme file. It probably works best to copy this theme file and update it to your requirements. The excellent theming guide is your go-to document for this task:
https://github.com/asciidoctor/asciidoctor-pdf/blob/master/docs/theming-guide.adocOnce you updated your custom theme, you run asciidoctor-pdf on the command line and reference the theme. For example:
asciidoctor-pdf -a pdf-stylesdir=~/asciidoctor-pdf/themes -a pdf-style=custom_theme.yml -o ~/asciidoctor-pdf/files/output.pdf input.adoc
I am not sure if this helps.
Marc.