A file with RTF file extension is Rich Text Format file. This is different from plain text files because it can withstand formatting such as bold and italic, plus different fonts and sizes, and images.
RTF files are very useful, because many programs supporting them. This means you can create RTF files in one program on a particular operating system, such as macOS, and then open the same RTF file on Windows or Linux and make it basically look the same.
How to open RTF file
The easiest way to open RTF files in Windows is to use WordPad because it has been previously installed. However, text editors and other word processors work basically in the same way, such as LibreOffice, OpenOffice, AbleWord, Jarte, AbiWord, WPS Office, and FreeOffice SoftMaker.

Zoho Docs and Google Docs are two ways you can open and edit RTF files online.
Tips: If you use Google Docs to edit RTF files, you must first upload them to your Google Drive account via the New menu> File upload. Then, right-click the file and select Open with> Google Docs.
Note: It is important to realize that not every program that supports RTF files can view files in the same way. This is because some programs do not support the newer RTF format specifications. More about that below.
Some other free methods for opening RTF files include using Microsoft Word or Corel WordPerfect.
Some of the Windows RTF editors also work with Linux and Mac. If you use MacOS, you can also use Apple TextEdit or Apple Pages to open RTF files.
Tip: If your RTF file is open in the program which you do not want to use; see How to Change the Default Program, for certain File Extensions in Windows. For example, making those changes will help if you want to edit your RTF file in Notepad but instead of opening it in OpenOffice Writer.
Read more: How to Open DOCX File
How to Convert RTF Files
The fastest way to convert this type of file is to use an online RTF converter such as FileZigZag. You can save RTF as DOC, PDF, TXT, ODT, or HTML files. Another way to convert RTF to PDF online, or to PNG, PCX, or PS, is to use Zamzar.

Doxillion is a free document file converter that can convert RTF to DOCX and a number of other document formats.
Another way to convert RTF files is to use one of the RTF editors from above. With the file open, use the File menu or some sort of Export option to save RTF to a different file format.
More information about RTF format
Firstly, the RTF format was used in 1987, but stopped being updated by Microsoft in 2008. Since then, there have been several revisions to the format. What determines whether a document editor will display RTF files in the same way as they are made depends on the version of RTF used.
For example, when you can insert images in RTF files, not all readers know how to display them because not all are updated to the latest RTF specifications. When this happens, the image will not be displayed at all.
RTF files have been used for Windows help files but have since been replaced by Microsoft Compiled HTML Help files that use the CHM file extension.
The first of RTF version was released in 1987; and then used by MS Word 3. From 1989 to 2006, versions 1.1 through 1.91 were released, with the last RTF version supporting things like XML markup, XML custom tags, password protection, and mathematical elements.
Because the RTF format is based on XML and not binary, you can actually read content when opening files in a plain text editor such as Notepad.
RTF files do not support macros but that does not mean that “.RTF” files are macro-safe. For example, an MS Word file containing macros can be renamed to have a .RTF file extension so that it looks safe, but then when opened in MS Word, the macro can still run normally because it’s not really an RTF file.