- When you visit a PDF or DVI file, Emacs automatically switches to
-DocView mode. When you visit a Postscript file, Emacs switches to PS
-mode, a major mode for editing Postscript files as text; however, it
-also enables DocView minor mode, so you can type @kbd{C-c C-c} to view
-the document with DocView. (PDF and DVI files, unlike Postscript
-files, are not usually human-editable.) In either case, repeating
-@kbd{C-c C-c} (@code{doc-view-toggle-display}) toggles between DocView
-and the file text.
+ When you visit a document file with the exception of Postscript
+files, Emacs automatically switches to DocView mode if possible
+@footnote{The needed external tools for this document type have to be
+available, emacs needs to run in a graphical frame, and PNG image
+support has to be compiled into emacs. If any of these requirements
+is not fulfilled, DocView falls back to an appropriate mode.}. When
+you visit a Postscript file, Emacs switches to PS mode, a major mode
+for editing Postscript files as text; however, it also enables DocView
+minor mode, so you can type @kbd{C-c C-c} to view the document with
+DocView. (PDF and DVI files, unlike Postscript files, are not usually
+human-editable.) In either case, repeating @kbd{C-c C-c}
+(@code{doc-view-toggle-display}) toggles between DocView and the file
+text.