Exporting convertToScreenPoint() and adding an optional viewport argument to function.

Author: Angelina1984

dist/pdf-annotate.js

@@ -4,11 +4,16 @@ import render from './render';
 import UI from './UI';
 import config from './config';
 import uuid from './utils/uuid';
-import { findAnnotationAtPoint, findSVGContainer } from './UI/utils';
+import { 
+  findAnnotationAtPoint, 
+  findSVGContainer,
+  convertToScreenPoint
+} from './UI/utils';
 
 export default {
   findAnnotationAtPoint,
   findSVGContainer,
+  convertToScreenPoint,
 
   /**
    * Abstract class that needs to be defined so PDFJSAnnotate