What is MIME type "application/x-pdf"?

A MIME type is a string that tells browsers and other tools how to handle a particular kind of file.

The MIME type application/x-pdf identifies files that use the Portable Document Format.
It tells apps that the file is a document meant for viewing with a PDF reader. Files marked with this type are processed correctly by browsers, email clients, and various software tools.

Primary use: It signals that the file is a PDF document intended for display or printing.
Technical functionality: It aids systems in choosing the right viewer or plugin to render the document accurately.
Additional use cases: It is used in web pages and email attachments to ensure consistent handling of PDF data.

Some systems now prefer the standard application/pdf MIME type. However, application/x-pdf is still encountered in legacy environments and setups.
For more on file types and handling, visit Filext.

Associated file extensions

.pdf

Usage Examples

HTTP Header

When serving content with this MIME type, set the Content-Type header:


    Content-Type: application/x-pdf

HTML

In HTML, you can specify the MIME type in various elements:


    <a href="file.dat" type="application/x-pdf">Download file</a>

Server-side (Node.js)

Setting the Content-Type header in Node.js:


    const http = require('http');    
    
    http.createServer((req, res) => {    
      res.setHeader('Content-Type', 'application/x-pdf');    
      res.end('Content here');    
    }).listen(3000);

Associated file extensions

.pdf

FAQs

What is the difference between application/x-pdf and application/pdf?

application/pdf is the standard, IANA-registered MIME type for PDF documents, while application/x-pdf is a non-standard or experimental variation. The x- prefix usually denotes experimental types, and while many legacy systems still use it, modern applications prefer the standard version.

Should I configure my web server to use application/x-pdf?

generally, no. You should configure your server to serve pdf files as application/pdf for maximum compatibility with modern browsers and PDF viewers. Use application/x-pdf only if you are supporting specific legacy software that explicitly requires it.

Why do some browsers download the PDF instead of opening it?

This can happen if the browser does not recognize application/x-pdf as a natively renderable format, unlike the standard type. It can also occur if the server sends a Content-Disposition: attachment header, forcing the file to be saved rather than displayed.

How do I add support for application/x-pdf in Apache?

If you must support this type, you can add AddType application/x-pdf .pdf to your .htaccess or server configuration file. However, ensure this does not conflict with the standard mapping for application/pdf, which is preferred for general web traffic.

Are there security risks associated with application/x-pdf?

The MIME type itself is just a label, but PDF files can contain malicious JavaScript or exploits. Whether labeled as application/x-pdf or the standard type, you should always treat PDF attachments from unknown sources with caution and keep your viewer software updated.

Does Nginx support application/x-pdf by default?

Most default Nginx mime.types files map the .pdf extension to application/pdf. To use the x-pdf variant, you would need to manually edit your configuration to map the extension to application/x-pdf, though this is rarely recommended for public websites.

General FAQ

What is a MIME type?

A MIME (Multipurpose Internet Mail Extensions) type is a standard that indicates the nature and format of a document, file, or assortment of bytes. MIME types are defined and standardized in IETF's RFC 6838.

MIME types are important because they help browsers and servers understand how to process a file. When a browser receives a file from a server, it uses the MIME type to determine how to display or handle the content, whether it's an image to display, a PDF to open in a viewer, or a video to play.

MIME types consist of a type and a subtype, separated by a slash (e.g., text/html, image/jpeg, application/pdf). Some MIME types also include optional parameters.

How do I find the MIME type for a file?

You can check the file extension or use a file identification tool such as file --mime-type on the command line. Many programming languages also provide libraries to detect MIME types.

Why are multiple MIME types listed for one extension?

Different applications and historical conventions may use alternative MIME identifiers for the same kind of file. Showing them all helps ensure compatibility across systems.