Index: lib/redmine/export/pdf.rb
===================================================================
--- lib/redmine/export/pdf.rb	(revision 12037)
+++ lib/redmine/export/pdf.rb	(working copy)
@@ -113,6 +113,8 @@
         end
 
         def formatted_text(text)
+          # Remove {{collapse()}} tags, but keep content
+          text.gsub!(/\{\{collapse\(.*?\)(.*?)\}\}/m, '\1')
           html = Redmine::WikiFormatting.to_html(Setting.text_formatting, text)
           # Strip {{toc}} tags
           html.gsub!(/<p>\{\{([<>]?)toc\}\}<\/p>/i, '')