The template files can be found within the /plugins/dk-pdf/templates/ directory.

Override templates in Theme

You can customize DK PDF template files in an upgrade safe way through overrides. Simply copy the desired templates into a directory within your theme named /dkpdf, keeping the same file structure.

Example:

Copy plugins/dk-pdf/templates/dkpdf-index.php to themes/your-theme/dkpdf/dkpdf-index.php

Override templates in Child Theme

DK PDF allows override templates in Child Themes too.

Example:

Copy plugins/dk-pdf/templates/dkpdf-index.php to themes/your-child-theme/dkpdf/dkpdf-index.php

More info about Child Themes (WordPress Theme Handbook)