diff --git a/htdocs/core/actions_massactions.inc.php b/htdocs/core/actions_massactions.inc.php
index c067ee2bc56..e19530ec209 100644
--- a/htdocs/core/actions_massactions.inc.php
+++ b/htdocs/core/actions_massactions.inc.php
@@ -1028,14 +1028,18 @@ if (!$error && $massaction == "builddoc" && $permissiontoread && !GETPOST('butto
 				$input_files .= ' '.escapeshellarg($f);
 			}
 
-			$cmd = 'pdftk '.escapeshellarg($input_files).' cat output '.escapeshellarg($file);
+			$cmd = 'pdftk ' . $input_files . ' cat output '.escapeshellarg($file);
 			exec($cmd);
 
-			if (!empty($conf->global->MAIN_UMASK))
-				@chmod($file, octdec($conf->global->MAIN_UMASK));
-
-			$langs->load("exports");
-			setEventMessages($langs->trans('FileSuccessfullyBuilt', $filename.'_'.dol_print_date($now, 'dayhourlog')), null, 'mesgs');
+			// check if pdftk is installed
+			if (file_exists($file)) {
+				if (!empty($conf->global->MAIN_UMASK))
+					@chmod($file, octdec($conf->global->MAIN_UMASK));
+				$langs->load("exports");
+				setEventMessages($langs->trans('FileSuccessfullyBuilt', $filename.'_'.dol_print_date($now, 'dayhourlog')), null, 'mesgs');
+			} else {
+				setEventMessages($langs->trans('ErrorPDFTkOutputFileNotFound'), null, 'errors');
+			}
 		}
 		else
 		{
diff --git a/htdocs/langs/en_US/main.lang b/htdocs/langs/en_US/main.lang
index 8c992bf91ca..532edcb6a67 100644
--- a/htdocs/langs/en_US/main.lang
+++ b/htdocs/langs/en_US/main.lang
@@ -840,6 +840,7 @@ Sincerely=Sincerely
 ConfirmDeleteObject=Are you sure you want to delete this object?
 DeleteLine=Delete line
 ConfirmDeleteLine=Are you sure you want to delete this line?
+ErrorPDFTkOutputFileNotFound=Error: the file was not generated. Please check that the 'pdftk' command is installed in a directory included in the $PATH environment variable (linux/unix only) or contact your system administrator.
 NoPDFAvailableForDocGenAmongChecked=No PDF were available for the document generation among checked record
 TooManyRecordForMassAction=Too many records selected for mass action. The action is restricted to a list of %s records.
 NoRecordSelected=No record selected
@@ -1032,4 +1033,4 @@ DeleteFileHeader=Confirm file delete
 DeleteFileText=Do you really want delete this file?
 ShowOtherLanguages=Show other languages
 SwitchInEditModeToAddTranslation=Switch in edit mode to add translations for this language
-NotUsedForThisCustomer=Not used for this customer
\ No newline at end of file
+NotUsedForThisCustomer=Not used for this customer
diff --git a/htdocs/modulebuilder/index.php b/htdocs/modulebuilder/index.php
index 89a1d20628e..7e6355b2a30 100644
--- a/htdocs/modulebuilder/index.php
+++ b/htdocs/modulebuilder/index.php
@@ -1060,7 +1060,7 @@ if ($dirins && ($action == 'droptable' || $action == 'droptableextrafields') &&
 	$objectname = $tabobj;
 
 	$arrayoftables = array();
-	if ($action == 'droptable') $arrayoftables[] = MAIN_DB_PREFIX.strtoslower($module).'_'.strtolower($tabobj);
+	if ($action == 'droptable') $arrayoftables[] = MAIN_DB_PREFIX.strtolower($module).'_'.strtolower($tabobj);
 	if ($action == 'droptableextrafields') $arrayoftables[] = MAIN_DB_PREFIX.strtolower($module).'_'.strtolower($tabobj).'_extrafields';
 
 	foreach ($arrayoftables as $tabletodrop)
diff --git a/htdocs/product/class/html.formproduct.class.php b/htdocs/product/class/html.formproduct.class.php
index 0eeddd15c07..903eedd3e8a 100644
--- a/htdocs/product/class/html.formproduct.class.php
+++ b/htdocs/product/class/html.formproduct.class.php
@@ -237,13 +237,14 @@ class FormProduct
 	 */
 	public function selectWarehouses($selected = '', $htmlname = 'idwarehouse', $filterstatus = '', $empty = 0, $disabled = 0, $fk_product = 0, $empty_label = '', $showstock = 0, $forcecombo = 0, $events = array(), $morecss = 'minwidth200', $exclude = '', $showfullpath = 1, $stockMin = false, $orderBy = 'e.ref')
 	{
-		global $conf, $langs, $user;
+		global $conf, $langs, $user, $hookmanager;
 
 		dol_syslog(get_class($this)."::selectWarehouses $selected, $htmlname, $filterstatus, $empty, $disabled, $fk_product, $empty_label, $showstock, $forcecombo, $morecss", LOG_DEBUG);
 
 		$out = '';
 		if (empty($conf->global->ENTREPOT_EXTRA_STATUS)) $filterstatus = '';
         if (!empty($fk_product))  $this->cache_warehouses = array();
+
 		$this->loadWarehouses($fk_product, '', $filterstatus, true, $exclude, $stockMin, $orderBy);
 		$nbofwarehouses = count($this->cache_warehouses);
 
@@ -287,6 +288,28 @@ class FormProduct
 		$out .= '</select>';
 		if ($disabled) $out .= '<input type="hidden" name="'.$htmlname.'" value="'.(($selected > 0) ? $selected : '').'">';
 
+        $parameters = array(
+            'selected' => $selected,
+            'htmlname' => $htmlname,
+            'filterstatus' => $filterstatus,
+            'empty' => $empty,
+            'disabled ' => $disabled,
+            'fk_product' => $fk_product,
+            'empty_label' => $empty_label,
+            'showstock' => $showstock,
+            'forcecombo' => $forcecombo,
+            'events' => $events,
+            'morecss' => $morecss,
+            'exclude' => $exclude,
+            'showfullpath' => $showfullpath,
+            'stockMin' => $stockMin,
+            'orderBy' => $orderBy
+        );
+
+        $reshook = $hookmanager->executeHooks('selectWarehouses', $parameters, $this);
+        if ($reshook > 0) $out = $hookmanager->resPrint;
+		elseif ($reshook == 0) $out .= $hookmanager->resPrint;
+
 		return $out;
 	}