diff --git a/README.org b/README.org
index a7d02a2..a6b9af0 100644
--- a/README.org
+++ b/README.org
@@ -3241,6 +3241,25 @@ Listing [[lst:configure-goto-address-mode]]:
         (kbd "C-c C-o") #'goto-address-at-point)))
 #+end_src
 
+*** [[https://en.wikipedia.org/wiki/Media_type#Mailcap][Mailcap]]
+:PROPERTIES:
+:CUSTOM_ID: sec:mailcap
+:END:
+
+Extension packages as [[info:emacs#EWW][EWW (info)]], [[info:emacs#Gnus][Gnus (info)]], and [[info:org#Top][Org (info)]] rely on a [[https://en.wikipedia.org/wiki/Media_type#Mailcap][mailcap]]
+file to know what application should open a specific media file type.  Listing
+[[lst:tangle-mailcap-file]] specifies =emacsclient= as the application to open PDF
+files.
+
+#+caption[Tangle =mailcap= file]:
+#+caption: Tangle =mailcap= file.
+#+name: lst:tangle-mailcap-file
+#+begin_src org :tangle ~/.mailcap
+  # https://emacs.stackexchange.com/a/24502 answers the question:
+  # How to use pdf-tools (pdf-view-mode) in emacs?
+  application/pdf; emacsclient %s
+#+end_src
+
 ** [[https://github.com/skeeto/elfeed#readme][Elfeed: Emacs web feed reader]]
 :PROPERTIES:
 :CUSTOM_ID: sec:emacs-web-feed-reader