diff --git a/config/configuration.yml.example b/config/configuration.yml.example
index cdfd516b5..5366a2911 100644
--- a/config/configuration.yml.example
+++ b/config/configuration.yml.example
@@ -242,6 +242,7 @@ default:
   # Absolute path (e.g. /usr/local/bin/pandoc) to the Pandoc command
   # used to convert supported attachments to Markdown for preview.
   #pandoc_command:
+  #pandoc_extensions: .docx .xlsx .pptx .odt
 
 # specific configuration options for production environment
 # that overrides the default ones
diff --git a/lib/redmine/markdownizer.rb b/lib/redmine/markdownizer.rb
index 898ef4a9b..112ed02c9 100644
--- a/lib/redmine/markdownizer.rb
+++ b/lib/redmine/markdownizer.rb
@@ -27,7 +27,7 @@ module Redmine
 
     COMMAND = (Redmine::Configuration['pandoc_command'] || 'pandoc').freeze
     MAX_PREVIEW_SIZE = 100.kilobytes
-    SUPPORTED_EXTENSIONS = %w(.doc .docx .xls .xlsx .ppt .pptx .odt .ods .odp).freeze
+    SUPPORTED_EXTENSIONS = (Redmine::Configuration['pandoc_extensions'] || %w(.docx .xlsx .pptx .odt)).freeze
 
     def self.supports?(filename)
       SUPPORTED_EXTENSIONS.include?(File.extname(filename.to_s).downcase)
@@ -39,28 +39,29 @@ module Redmine
 
       directory = File.dirname(target)
       FileUtils.mkdir_p(directory)
-      cmd = "#{shell_quote COMMAND} #{shell_quote source} -t gfm"
+      args = [COMMAND, source, "-t", "gfm"]
       pid = nil
       output = Tempfile.new('markdownized-preview')
 
       begin
         Timeout.timeout(Redmine::Configuration['thumbnails_generation_timeout'].to_i) do
-          pid = Process.spawn(cmd, out: output.path)
+          pid = Process.spawn(*args, out: output.path)
           _, status = Process.wait2(pid)
           unless status.success?
-            logger.error("Markdown conversion failed (#{status.exitstatus}):\nCommand: #{cmd}")
+            logger.error("Markdown conversion failed (#{status.exitstatus}):\nCommand: #{args.shelljoin}")
             return nil
           end
         end
       rescue Timeout::Error
         Process.kill('KILL', pid) if pid
-        logger.error("Markdown conversion timed out:\nCommand: #{cmd}")
+        logger.error("Markdown conversion timed out:\nCommand: #{args.shelljoin}")
         return nil
       rescue => e
-        logger.error("Markdown conversion failed:\nCommand: #{cmd}\nException was: #{e.message}")
+        logger.error("Markdown conversion failed:\nCommand: #{args.shelljoin}\nException was: #{e.message}")
         return nil
       ensure
         output.close
+        Process.detach(pid)
       end
 
       preview = File.binread(output.path, MAX_PREVIEW_SIZE + 1) || +""
@@ -74,8 +75,8 @@ module Redmine
       return @available if defined?(@available)
 
       begin
-        `#{shell_quote COMMAND} --version`
-        @available = $?.success?
+        version = `#{shell_quote COMMAND} --version`[/pandoc\s+([\d.]+)/, 1].split('.').map(&:to_i)
+        @available = ($?.success? && (version <=> [3, 9]) >= 0) # Pandoc.version >= 3.9
       rescue
         @available = false
       end