To read a PDF-file online, you need to use some specialized online PDF-readers, which can be downloaded and used for free on the Internet. Here are some commonly used online PDF-readers: 1. Android Reader: Android Reader is a powerful reader that can read, annotate, and edit PDF-files. It's free to download and use, and can be downloaded from the official website of the company. 2. Google Chrome-based browser extension: The Google Chrome-based browser has an extension called the "PDF-reader" that allows you to read PDF-based files. This extension is free to download and use. You can search for it in the browser. 3. The browser extension for FireFox: The browser for FireFox also has an extension called PDF-X that allows you to read and annotate PDF-s. This extension required a fee to download and use. 4. readerio:readerio is a free online reader that can read and manage PDF-files. It supports a variety of file format, including Word documents, Excel documents, pictures and videos. Using these online PDF-readers, you can choose the reading mode, annotation function, search and filter according to different needs to easily read PDF-files online.