This LaTeX class I use to format covers for my books, which I sell on Amazon. The problem this class solves is the necessity to change the size of the cover PDF respectfully to the number of pages in the book — the bigger the book, the larger must be the cover. The provided class makes necessary calculations on-fly, using the qpdf tool. Obviously, you need to have it installed. Also, you must run pdflatex with the --shell-escape option, in order to allow LaTeX to run qpdf.

First, install it from CTAN and then use in the preamble:

\documentclass[pdf=my-book.pdf]{kdpcover}
\begin{document}
% Here you print the cover as you wish, but I recommend
% you to use the commands available in the class, such as:
\putSpine{my book, vol. 1}
\putAuthor{Yegor Bugayenko}
\end{document}

If you want to contribute yourself, make a fork, then create a branch, then run make in the root directory. It should compile everything without errors. If not, submit an issue and wait. Otherwise, make your changes and then run make again. If the build is still clean, submit a pull request.