Files with an HTM or HTML extension are Hypertext Markup Language files that are standard web pages. Because HTM files are text files, they contain only text as well as text links to other external files. For example, the pictures in this article. HTM and HTML files can contain links to other types of files - for example, video, CSS or JS files. You can open a file with the HTML extension using various browsers such as Mozilla Firefox and Google Chrome, as well as Edge, Internet Explorer, and so on. This file format can be edited in a text editor, since the .html file is represented by a standard text document.
The Portable Document Format (PDF) is a versatile file format that preserves the fonts, images, and layout of the original document, regardless of which of many platforms and which of many applications the document was created on. It was initiated by Adobe and was originally intended for electronic presentation of printed materials. PDFs look the same no matter what device they are viewed on. Whether you're using Windows 10, Mac, Chrome OS, Android, Windows Phone, iPad, or Windows XP - on any software or hardware, PDFs remain the same.