<p>When working with PDFs, I've run across the MIME types <code>application/pdf</code> and <code>application/x-pdf</code> among others. </p>

<p>Is there a difference between these two types, and if so what is it? Is one preferred over the other?</p>

<p>I'm working on a web app which must deliver huge amounts of PDFs and I want to do it the correct way, if there is one.</p>

The standard Media Type (formerly known as MIME types) is
```
application/pdf
```
. The assignment is defined in
RFC 3778, The application/pdf Media Type
, referenced from the
Media Types registry
.
Media Types are controlled by a standards body, The
Internet Assigned Numbers Authority
(IANA). This is the same organization that manages the root name servers and the IP address space.
The use of
```
x-pdf
```
predates the standardization of the Media Type for PDF. Media Types in the
```
x-
```
namespace are considered experimental, just as those in the
```
vnd.
```
namespace are considered vendor-specific.
```
x-pdf
```
might be used for compatibility with old software.