A PHP file is like any other text file that you may be familiar with. Therefore, you can use readily-available programs such as Notepad on Windows, or TextEdit on a Mac, to open a PHP file. You can also use these programs to edit and save the PHP file. Additionally, there is a multitude of programs specifically designed for editing PHP files.
To open a PHP file in Notepad, first launch the Notepad application. In Notepad, select File, Open in the menu bar. Navigate to the folder where you saved the PHP file. You may notice that the file does not appear in the list. In order to see the PHP file, you will need to change the extension to All Files using the drop-down next to the File Name field. Now you should be able to select your PHP file, and click Open.
To open a PHP file in TextEdit, navigate to where the PHP file is located. Then, secondary click the file and select Open With, then TextEdit.
Special software exists to allow for easier viewing and editing of PHP files. One common feature of these programs is syntax highlighting. Syntax highlighting color-codes certain words, phrases, and characters that have special meaning in the programming or scripting language. While these programs may offer features that are not found in Notepad or TextEdit, they perform the same basic function of editing a text file. As such, you can open and save PHP files in the same way as described above.
Since PHP is designed to work alongside standard HTML, PHP files are often interwoven with HTML. In some cases, the majority of a PHP file may actually be HTML.