Issue #1866174: Improve comments

fillpdf.module

@@ -2009,7 +2009,13 @@ function fillpdf_load($fid, $reset = FALSE, $process_replacements = TRUE) {
 }
 
 /**
+ * Test whether the pdftk path is valid.
  *
+ * @param string $pdftk_path
+ *   The path to test.
+ *
+ * @return bool
+ *   TRUE if the path is the pdftk binary, FALSE otherwise.
  */
 function fillpdf_pdftk_check($pdftk_path = 'pdftk') {
   // An empty value means we should leave it to the PATH.
@@ -2019,6 +2025,7 @@ function fillpdf_pdftk_check($pdftk_path = 'pdftk') {
   $output = array();
   $status = NULL;
   exec($pdftk_path, $output, $status);
+  // Check the exit status.
   if (in_array($status, array(126, 127))) {
     return FALSE;
   }