diff --git a/Zotero/Scenes/Detail/PDF/PDFCoordinator.swift b/Zotero/Scenes/Detail/PDF/PDFCoordinator.swift
index f8b9c53d5..fde63cf28 100644
--- a/Zotero/Scenes/Detail/PDF/PDFCoordinator.swift
+++ b/Zotero/Scenes/Detail/PDF/PDFCoordinator.swift
@@ -27,6 +27,7 @@ protocol PdfReaderCoordinatorDelegate: AnyObject {
     func show(error: PDFDocumentExporter.Error)
     func share(url: URL, barButton: UIBarButtonItem)
     func share(text: String, rect: CGRect, view: UIView, userInterfaceStyle: UIUserInterfaceStyle)
+    func lookup(text: String, rect: CGRect, view: UIView, userInterfaceStyle: UIUserInterfaceStyle)
     func showDeletedAlertForPdf(completion: @escaping (Bool) -> Void)
     func showSettings(with settings: PDFSettings, sender: UIBarButtonItem) -> ViewModel<ReaderSettingsActionHandler>
     func showReader(document: Document, userInterfaceStyle: UIUserInterfaceStyle)
@@ -303,6 +304,18 @@ extension PDFCoordinator: PdfReaderCoordinatorDelegate {
         self.share(item: text, sourceView: .view(view, rect), userInterfaceStyle: userInterfaceStyle)
     }
 
+    func lookup(text: String, rect: CGRect, view: UIView, userInterfaceStyle: UIUserInterfaceStyle) {
+        DDLogInfo("PDFCoordinator: show lookup")
+        // When presented as a popover, UIReferenceLibraryViewController ignores overrideUserInterfaceStyle, so we wrap it in a navigation controller to force it.
+        let controller = UINavigationController(rootViewController: UIReferenceLibraryViewController(term: text))
+        controller.setNavigationBarHidden(true, animated: false)
+        controller.overrideUserInterfaceStyle = userInterfaceStyle
+        controller.modalPresentationStyle = .popover
+        controller.popoverPresentationController?.sourceView = view
+        controller.popoverPresentationController?.sourceRect = rect
+        self.navigationController?.present(controller, animated: true, completion: nil)
+    }
+
     func show(error: PDFReaderState.Error) {
         let title: String
         let message: String
diff --git a/Zotero/Scenes/Detail/PDF/Views/PDFDocumentViewController.swift b/Zotero/Scenes/Detail/PDF/Views/PDFDocumentViewController.swift
index a2dca3f06..339d6efca 100644
--- a/Zotero/Scenes/Detail/PDF/Views/PDFDocumentViewController.swift
+++ b/Zotero/Scenes/Detail/PDF/Views/PDFDocumentViewController.swift
@@ -782,6 +782,9 @@ extension PDFDocumentViewController: PDFViewControllerDelegate {
                         return action
                     }
 
+                case .PSPDFKit.accessibility:
+                    return action
+
                 case .share:
                     guard action.identifier == .PSPDFKit.share else { return nil }
                     return action.replacing(handler: { [weak self] _ in
@@ -796,6 +799,17 @@ extension PDFDocumentViewController: PDFViewControllerDelegate {
 
                 case .pspdfkitActions:
                     switch action.identifier {
+                    case .PSPDFKit.define:
+                        return action.replacing(title: L10n.lookUp, handler: { [weak self] _ in
+                            guard let self else { return }
+                            coordinatorDelegate?.lookup(
+                                text: glyphs.text,
+                                rect: pageView.convert(glyphs.boundingBox, from: pageView.pdfCoordinateSpace),
+                                view: pageView,
+                                userInterfaceStyle: viewModel.state.settings.appearanceMode.userInterfaceStyle
+                            )
+                        })
+
                     case .PSPDFKit.searchDocument:
                         return action.replacing(handler: { [weak self] _ in
                             guard let self, let pdfController else { return }