diff --git a/functions/pdf.xml b/functions/pdf.xml
index 850276d68d..a8c1241d97 100644
--- a/functions/pdf.xml
+++ b/functions/pdf.xml
@@ -18,6 +18,15 @@
     the test programm in configure. You will have to create a symbolic
     link from libpdf.so to libpdf2.01.so.).
    </simpara>
+   <simpara>
+    Version 2.20 of pdflib has introduced more changes to its API and
+    support for chinese and japanese fonts. This unfortunately causes
+    some changes of the pdf module of php4 (not php3). If you use pdflib 2.20
+    handle the in memory generation of PDF documents with care. Until
+    pdflib 3.0 is released it might be unstable. The encoding parameter
+    of <function>pdf_set_font</function> has changed to a string. This
+    means that instead of e.g. 4 you have to use 'winansi'.
+   </simpara>
    <simpara>
     Please consult the excellent documentation for
     pdflib shipped with the source distribution of pdflib.
@@ -710,11 +719,15 @@ fclose($fp);
      current font face, font size and encoding. If you use pdflib 0.6
      you will need to
      provide the Adobe Font Metrics (afm-files) for the font in the
-     font path (default is ./fonts). The fourth parameter
+     font path (default is ./fonts). If you use php3 or a version of
+     pdflib older than 2.20 the fourth parameter
      <parameter>encoding</parameter> can take the following values:
      0 = builtin, 1 = pdfdoc, 2 = macroman, 3 = macexpert, 4 = winansi.
      An encoding greater than 4 and less than 0 will default to winansi.
-     winansi is often a good choice. If the last parameter is set to
+     winansi is often a good choice.
+     If you use php4 and a version of pdflib >= 2.20 the encoding parameter
+     has changed to a string. Use 'winansi', 'builtin' etc. instead.
+     If the last parameter is set to
      1 the font is embedded into the pdf document otherwise it is not.
      To embed a font is usually a good idea if the font is not widely spread
      and you cannot ensure that the person watching your document has