PDF Tools, is a simple add-on which allows you to easily manipulate (convert, resize, merge, etc.) PDF documents right in your browser. It uses an open-source software called Ghostscript. Ghostscript is an engine for interpreting portable document formats (PDF) and postscript (PS). In order to get more info about Ghostscript please read this (https://en.wikipedia.org/wiki/Ghostscript) Wikipedia page. To download and install Ghostscript on your machine, please visit this (https://www.ghostscript.com/download/gsdnld.html) page. This add-on uses nativeMessaging (https://developer.chrome.com/apps/nativeMessaging) technology to communicate with Ghostscript client on your machine. Before using this add-on, you need to install Ghostscript on your machine. You also need the native client patch in order to build the communication between Ghostscript and your browser. Please visit this (https://github.com/alexmarcoo-nt/open-in-native-client/releases) GitHub repo and download the related patch for your machine. Follow the instruction in the above GitHub page in order to install the patch in your system. After installing, the "PDF Tools" add-on in your browser can communicate with the Ghostscript client on your machine (Window, Linux, or Mac). If you have a feature request or found a bug to report, please fill the bug report form in the add-on's homepage (https://mybrowseraddon.com/pdf-tools.html).