Changing format of paragraph skip for a 400-pages document

Question

I am writing a long LaTeX document using the book documentclass, and after having typed already almost 400 pages, I have decided I want to change the format for new paragraphs to be more similar to the letter style, meaning that instead of an indented line, I would like to have some vertical space between paragraphs (not as much as a whole line) and the new paragraph to begin without indentation.

I could do this by placing \noindent at the beginning of each paragraph, and maybe adjusting the space with \vspace, but I imagine there is a better way than doing this one paragraph at a time for over 400 pages…

Answer 1

You can do \usepackage{parskip}, but, please, compare the two images below: the shorter your paragraph, more white bands across the page will appear. Maybe good for a letter; for books, I strongly adverse it.

For the first image I commented out \usepackage{parskip}.

\documentclass[a4paper]{book}
\usepackage{parskip}

\usepackage{lipsum} % for mock text

\begin{document}

\lipsum

\end{document}