Adobe Acrobat PDF pdf application/pdf & application/x-pdf

• thomas-fahle.de/pub/perl/MIME/MIME_Basics.html
• en.wikipedia.org/wiki/MIME (erspar dir die deutsche version)

Content-Transfer-Encoding
MIME (RFC 2045) defines a set of methods for representing binary data in ASCII text format. The content-transfer-encoding: MIME header indicates the method that has been used. Typically encountered values for this header include:
* 7bit - up to 998 octets per line of the code range [1..127]\{CR, NL}. This is the default value.
* 8bit - up to 998 octets per line of the code range [1..255]\{CR, NL}. This can be used only if both the sending and receiving mail transfer agents support the 8bit MIME transport SMTP extension.
* binary - any sequence of octets
* quoted-printable - used for text data consisting primarily of US-ASCII characters
* base64 - used for arbitrary binary data