Zotero is a free and open-source reference management software that is used to manage bibliographic data and related research materials such as PDF files). It was initially released in October 2006.
Web page: zotero.org
PDF (Portable Document Format) is a commonly used document format created by Adobe. Creating a PDF of a keyboard shortcut list may make it easier to print, quicker to open, and view offline. The PDF output is also without any ads, it's just the basic list presented in two or three columns.
Printing notice: Please consider environmental effect before printing on a paper.