diff --git a/pdfcleaner.cabal b/pdfcleaner.cabal
index cf49054..59681e0 100644
--- a/pdfcleaner.cabal
+++ b/pdfcleaner.cabal
@@ -50,6 +50,7 @@ executable sync
                      , Hufflepdf
                      , mtl
                      , soprano
+                     , text
                      , xml
   ghc-options:         -Wall
   hs-source-dirs:      src
diff --git a/src/ALTO.hs b/src/ALTO.hs
index b82bdba..9d677f1 100644
--- a/src/ALTO.hs
+++ b/src/ALTO.hs
@@ -1,6 +1,7 @@
 {-# LANGUAGE NamedFieldPuns #-}
 module ALTO (
       Collection
+    , ALTO_ID(..)
     , Words
     , collection
     , getWords
@@ -20,7 +21,10 @@ data Collection = Collection {
       path :: FilePath
     , pages :: Map Int FilePath
   }
-type Words = [(String, String)]
+newtype ALTO_ID = ALTO_ID {
+    altoID :: String
+  }
+type Words = [(String, ALTO_ID)]
 
 getWords :: Collection -> Int -> IO Words
 getWords (Collection {path, pages}) pageNumber = do
@@ -31,7 +35,7 @@ getWords (Collection {path, pages}) pageNumber = do
       t<$>["alto", "Layout", "Page", "PrintSpace", "TextBlock", "TextLine", "String"]
     wordOfElem element =
       case (getAttr "CONTENT" element, getAttr "ID" element) of
-        (Just content, Just elemID) -> return (content, elemID)
+        (Just content, Just elemID) -> return (content, ALTO_ID elemID)
         (Nothing, _) -> die $ "Missing CONTENT in word " ++ show element
         _ -> die $ "Missing ID in word " ++ show element
 
diff --git a/src/Sync.hs b/src/Sync.hs
index c73f64d..4da042a 100644
--- a/src/Sync.hs
+++ b/src/Sync.hs
@@ -1,51 +1,78 @@
 {-# LANGUAGE FlexibleContexts #-}
 module Main where
 
-import ALTO (Collection, collection, getWords)
+import ALTO (ALTO_ID(..), Collection, Words, collection, getWords)
+import Control.Monad.Except (MonadError(..), ExceptT(..))
 import Control.Monad.Except.IOH (handle)
-import Control.Monad.IO.Class (liftIO)
-import Control.Monad.Reader (runReaderT)
+import Control.Monad.IO.Class (MonadIO, liftIO)
 import Control.Monad.State (MonadState(..), evalStateT)
 import Control.Monad.Trans (lift)
 import qualified Data.ByteString.Char8 as BS (readFile)
-import qualified Data.ByteString.Lazy as Lazy (writeFile)
 import Data.Id (Id(..))
+import qualified Data.Id as Id(toList)
 import qualified Data.Map as Map (toList)
 import Data.OrderedMap (mapi)
-import PDF (Document, UnifiedLayers(..), parseDocument, render)
-import PDF.Box (Box(..), at)
-import PDF.Content.Operator (Instruction)
+import Data.Text (Text, pack, stripPrefix)
+import qualified Data.Text as Text (null, strip)
+import PDF (Document, UnifiedLayers(..), parseDocument)
+import PDF.Box (Box(..))
 import PDF.Content.Text (Chunks(..))
-import PDF.Layer (Layer)
 import PDF.Object (Object)
 import PDF.Pages (Contents(..), Pages(..), withFonts, withResources)
 import System.Environment (getArgs)
 import System.Exit (die)
 import Text.Printf (printf)
 
-synchronize :: Document -> Collection -> IO [(Id Object, Id Instruction, String)]
+type Mapping = (Id Object, Id Text, ALTO_ID)
+
+format :: Mapping -> String
+format (objectId, instructionId, ALTO_ID altoId) =
+  printf "%d,%d,%s" (getId objectId) (getId instructionId) altoId
+
+zipWithALTO :: (MonadIO m, MonadError String m, MonadState Words m) =>
+  Id Object -> [(Id Text, Text)]-> m ()
+zipWithALTO _ [] = return ()
+zipWithALTO objectId chunks@((chunkId, chunk):otherChunks) = popWord >>= zipWord
+  where
+    popWord = state (splitAt 1)
+    zipWord [(word, wordID)]
+      | pack word == chunk = do
+        liftIO . putStrLn $ format (objectId, chunkId, wordID)
+        zipWithALTO objectId otherChunks
+      | otherwise =
+          case stripPrefix (pack word) chunk of
+            Just stripped -> do
+              let editedChunks = (chunkId, stripped):otherChunks
+              liftIO . putStrLn $ format (objectId, chunkId, wordID)
+              zipWithALTO objectId editedChunks
+            Nothing -> zipWithALTO objectId chunks
+    zipWord _
+      | Text.null $ Text.strip chunk = zipWithALTO objectId otherChunks
+      | otherwise = throwError $
+        printf "Could not associate an ALTO_ID to all PDF chunks in object #%d. Remaining : %s\n"
+          (getId objectId)
+          (show chunks)
+
+synchronize :: Document -> Collection -> ExceptT String IO ()
 synchronize pdf alto =
-  (r UnifiedLayers pdf >>= withFonts extractFromLayer) `handle` die
+  r UnifiedLayers pdf >>= withFonts extractFromLayer
   where
     extractFromLayer layer =
-      r Pages layer >>= fmap concat . mapM extractFromPage . Map.toList
+      r Pages layer >>= mapM_ extractFromPage . Map.toList
     extractFromPage (pageNumber, page) = do
       altoWords <- liftIO $ getWords alto pageNumber
       withResources (flip evalStateT altoWords . extractWithResources) page
     extractWithResources page =
-      r Contents page >>= fmap concat . sequence . mapi extractFromObject
+      r Contents page >>= sequence_ . mapi extractFromObject
     extractFromObject objectId content =
-      lift (r Chunks content) >>= undefined
+      lift (r Chunks content) >>= zipWithALTO objectId . Id.toList
 
 processFiles :: FilePath -> FilePath -> IO ()
 processFiles inputFile altoDir = do
   pdf <- either die return . parseDocument =<< BS.readFile inputFile
   alto <- collection altoDir
   putStrLn "Object,Instruction,ALTO_ID"
-  mapM_ (putStrLn . format) =<< synchronize pdf alto
-  where
-    format (objectId, instructionId, altoId) =
-      printf "%d,%d,%s" (getId objectId) (getId instructionId) altoId
+  synchronize pdf alto `handle` die
 
 main :: IO ()
 main = do