Add close PDF button (close #7)

index.html

@@ -104,6 +104,7 @@ file, You can obtain one at http://mozilla.org/MPL/2.0/.
             <div class="btn-group me-2 mb-2" role="group" aria-label="First group">
                 <div class="btn btn-primary" onclick="addPDF();"><i class="fas fa-file-pdf"></i> Add PDF</div>
                 <div class="btn btn-primary" onclick="savePDF();"><i class="fas fa-save"></i> Save Signed PDF</div>
+                <div class="btn btn-primary" onclick="closePDF(true);"><i class="fas fa-trash"></i> Close PDF</div>
                 <div class="btn btn-primary" onclick="openSettingsModal();"><i class="fas fa-cog"></i> Settings</div>
             </div>
         </div>

js/pdf.js

@@ -30,6 +30,16 @@ function addPDF() {
     }, ".pdf");
 }
 
+function closePDF(showuserconfirm) {
+    if (showuserconfirm && !confirm("Are you sure you want to close? All unsaved changes will be lost.")) {
+        return;
+    }
+    disableGuideBox();
+    pageNumber = 0;
+    pdfDoc = null;
+    $("#page-canvas-container .page-canvas").remove();
+}
+
 function generatePDF() {
     var canvases = $("#page-canvas-container .page-canvas");
     const pdf = new jsPDF({
@@ -82,6 +92,7 @@ function makeAndSaveSignedPDF(pdf, savepath, callback) {
 }
 
 function savePDF() {
+    disableGuideBox();
     loadKeyFromLocalStorage(function (message, ok) {
         if (ok) {
             openSaveFileDialog(function (path) {