Which file format is typically used for storing plain text?

The file format .txt is primarily used for storing plain text. This format is designed to be a simple, straightforward way of saving text without any formatting, allowing for easy reading and editing across various text editors and operating systems. Plain text files contain unformatted text, making them lightweight and compatible with a wide range of software. This characteristic is essential for applications that require a focus on the text content without the complications of styles, fonts, or embedded images.

The other formats listed serve different purposes. .docx is a format used by Microsoft Word that supports advanced formatting and features such as images, tables, and other elements, making it unsuitable for plain text storage. .pdf is designed for presenting documents in a consistent format across various devices, often retaining complex layout and formatting, which is beyond the scope of plain text. .rtf, or Rich Text Format, allows some basic formatting while still being relatively compatible across different word processors, but it is not as simple as a .txt file. Thus, .txt stands out as the most appropriate choice for storing plain text.