PDF Glossary: Base64, Encoding, Data URI, and API Payload

A binary-to-text encoding scheme that represents any sequence of bytes using 64 printable ASCII characters, so binary files can travel through systems built for text.

The process of converting data from one representation to another — in this context, turning a PDF's binary bytes into a Base64 text string. See how Base64 encoding works for the mechanics.

The reverse of encoding: converting a Base64 string back into the original binary bytes. A correctly decoded PDF is byte-for-byte identical to the file that was encoded.

A string that combines a Base64-encoded value with a prefix describing its file type, in the form data:application/pdf;base64,.... Browsers and some viewers use the prefix to know how to render the data. See Base64 vs Data URI for when each form applies.

Data stored as raw bytes rather than human-readable text. A PDF, like any file format, is binary data at the byte level, regardless of how much text it visually contains.

A label such as application/pdf that identifies what kind of content a piece of data is. APIs and browsers use the MIME type to decide how to handle, display, or decode a file.

One or two = characters appended to a Base64 string when the original data length is not an exact multiple of 3 bytes. Padding fills out the last group of characters without adding real content.

The data sent in the body of an API request or response. A Base64-encoded PDF often lives inside a JSON payload as one field among several — see how to use a Base64 PDF in a JSON API request for a typical structure.