Fix file drag and drop (#2575)

# Description

Drag and drop only loading first page.

Closes #(2560)

## Checklist

- [ X] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [ X] I have performed a self-review of my own code
- [ X] I have attached images of the change if it is UI based
- [ X] I have commented my code, particularly in hard-to-understand
areas
- [ X] If my code has heavily changed functionality I have updated
relevant docs on [Stirling-PDFs doc
repo](https://github.com/Stirling-Tools/Stirling-Tools.github.io/blob/main/docs/)
- [ X] My changes generate no new warnings
- [ X] I have read the section [Add New Translation
Tags](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/HowToAddNewLanguage.md#add-new-translation-tags)
(for new translation tags only)

src/main/resources/templates/multi-tool.html

@@ -216,7 +216,7 @@
       undoManager
     )
 
-    fileDragManager.setCallback(async (files) => pdfContainer.addFilesFromFiles(files));
+    fileDragManager.setCallback(async (files) => pdfContainer.handleDroppedFiles(files));
     document.addEventListener('keydown', function(event) {
     let targetElementId = event.target.id;