Only install essential components on the server
Uninstall any services that are not vital for running the website. This will inevitably remove daemons (programs that constantly run in the background) which drain resources such as CPU power and RAM.
Generate PDFs outside of the CMS
Generating PDFs on-the-fly uses enormous amounts of CPU and RAM. Consequently, do not generate PDFs to order, page by page, but instead offer a few files generated and optimized outside of the CMS