converter.rb

# Install charlock_holmes gem:
#   sudo gem install charlock_holmes
# Set filename below and run script.

require 'charlock_holmes'

contents = File.read("documents.txt")
detection = CharlockHolmes::EncodingDetector.detect(contents)
p detection
new_contents = CharlockHolmes::Converter.convert contents, detection[:encoding], 'UTF-8'

File.open("documents_utf8.txt", 'w') {|f| f.write(new_contents) }