Issue #3274842: Create hook_fillpdf_populate_pdf_context_alter()

src/Controller/HandlePdfController.php

@@ -176,6 +176,11 @@ class HandlePdfController extends ControllerBase {
    */
   public function populatePdf() {
     $context = $this->linkManipulator->parseRequest($this->requestStack->getCurrentRequest());
+
+    // Create hook_fillpdf_populate_pdf_context_alter().
+    // Allow modules to alter $context.
+    $this->moduleHandler()->alter('fillpdf_populate_pdf_context', $context);
+
     $fillpdf_form = FillPdfForm::load($context['fid']);
     $entities = $this->contextManager->loadEntities($context);