Fixed error while loading file

EnvelopeGenerator.ReceiverUIBlazor/Pages/Index.razor

@@ -12,6 +12,11 @@
     <button class="btn secondary" @onclick="Download" disabled="@(!HasPdf)">Download</button>
 </div>
 
+@if (!string.IsNullOrWhiteSpace(ErrorMessage))
+{
+    <div class="error-banner">@ErrorMessage</div>
+}
+
 @if (!HasPdf)
 {
     <div class="drop-hint">Drop or select a PDF to start.</div>
@@ -96,6 +101,7 @@
     private double StartLeft;
     private double StartTop;
     private string TextValue = "Text";
+    private string? ErrorMessage;
 
     private bool HasPdf => !string.IsNullOrWhiteSpace(PdfBase64);
     private int DisplayPage => PageIndex + 1;
@@ -117,22 +123,41 @@
 
     private async Task HandleFileSelected(InputFileChangeEventArgs e)
     {
-        if (e.FileCount == 0)
+        ErrorMessage = null;
+
+        try
         {
-            return;
+            if (e.FileCount == 0)
+            {
+                return;
+            }
+
+            var file = e.File;
+            await using var stream = file.OpenReadStream(maxAllowedSize: 20 * 1024 * 1024);
+            using var ms = new MemoryStream();
+            await stream.CopyToAsync(ms);
+            PdfBase64 = Convert.ToBase64String(ms.ToArray());
+
+            // Show the canvas before we start rendering
+            await InvokeAsync(StateHasChanged);
+            await Task.Yield();
+
+            // Make sure pdf.js is ready
+            await JS.InvokeVoidAsync("pdfInterop.ensureReady");
+
+            var result = await JS.InvokeAsync<RenderResult>("pdfInterop.loadPdf", PdfBase64);
+            PageCount = result.Pages;
+            PageIndex = 0;
+
+            await RenderPage();
+        }
+        catch (Exception ex)
+        {
+            ErrorMessage = $"Fehler beim Laden der PDF: {ex.Message}";
+            PdfBase64 = null;
+            PageCount = 0;
+            PageIndex = 0;
         }
-
-        var file = e.File;
-        await using var stream = file.OpenReadStream(maxAllowedSize: 20 * 1024 * 1024);
-        using var ms = new MemoryStream();
-        await stream.CopyToAsync(ms);
-        PdfBase64 = Convert.ToBase64String(ms.ToArray());
-
-        var result = await JS.InvokeAsync<RenderResult>("pdfInterop.loadPdf", PdfBase64);
-        PageCount = result.Pages;
-        PageIndex = 0;
-
-        await RenderPage();
     }
 
     private async Task RenderPage()
@@ -142,10 +167,17 @@
             return;
         }
 
-        var viewport = await JS.InvokeAsync<ViewportInfo>("pdfInterop.renderPage", PageIndex, "pdf-canvas", ViewportWidthPx);
+        try
-        ViewportWidthPx = viewport.Width;
+        {
-        ViewportHeightPx = viewport.Height;
+            var viewport = await JS.InvokeAsync<ViewportInfo>("pdfInterop.renderPage", PageIndex, "pdf-canvas", ViewportWidthPx);
-        StateHasChanged();
+            ViewportWidthPx = viewport.Width;
+            ViewportHeightPx = viewport.Height;
+            StateHasChanged();
+        }
+        catch (Exception ex)
+        {
+            ErrorMessage = $"Fehler beim Rendern: {ex.Message}";
+        }
     }
 
     private void Reset()

EnvelopeGenerator.ReceiverUIBlazor/wwwroot/css/app.css

@@ -76,6 +76,15 @@ h1 {
     color: rgba(226, 232, 240, 0.8);
 }
 
+.error-banner {
+    margin-top: 8px;
+    padding: 10px 12px;
+    border-radius: 8px;
+    background: rgba(239, 68, 68, 0.12);
+    border: 1px solid rgba(239, 68, 68, 0.3);
+    color: #fecdd3;
+}
+
 .document-shell {
     position: relative;
     margin-top: 12px;

EnvelopeGenerator.ReceiverUIBlazor/wwwroot/index.html

@@ -6,9 +6,10 @@
     <title>Receiver UI (Blazor)</title>
     <base href="/" />
     <link rel="stylesheet" href="css/app.css" />
-    <script src="https://cdnjs.cloudflare.com/ajax/libs/pdf.js/4.0.269/pdf.min.js" integrity="sha512-tAqK8Nw4WnAnX/d+Q/FI+jTYfCLMVSX39kT9rCec8NLwlY+jIUUQx7TKfQvHr2SgVXmvGZtxPRQSf0oYAI7gCA==" crossorigin="anonymous" referrerpolicy="no-referrer"></script>
+        <!-- pdf.js 3.11 UMD + classic worker for compatibility; SRI removed to avoid digest mismatches -->
-    <script src="https://cdnjs.cloudflare.com/ajax/libs/pdf.js/4.0.269/pdf.worker.min.js" integrity="sha512-xS2zAkrE3zGZFNE2hCpL25O9P+hxKpADcDxpfoSr8q/kBDL/6Ht8OZODBM96KghAe8/powBPh6UT7aY4AsF38g==" crossorigin="anonymous" referrerpolicy="no-referrer"></script>
+        <script src="https://cdnjs.cloudflare.com/ajax/libs/pdf.js/3.11.174/pdf.min.js"></script>
-    <script src="https://unpkg.com/pdf-lib/dist/pdf-lib.min.js"></script>
+        <script src="https://cdnjs.cloudflare.com/ajax/libs/pdf.js/3.11.174/pdf.worker.min.js"></script>
+        <script src="https://unpkg.com/pdf-lib/dist/pdf-lib.min.js"></script>
     <script src="js/pdfInterop.js"></script>
 </head>
 <body>

EnvelopeGenerator.ReceiverUIBlazor/wwwroot/js/pdfInterop.js

@@ -1,8 +1,13 @@
 (function () {
+    // Stick to pdf.js 3.11 UMD + classic worker for compatibility.
+    const PDF_JS_SRC = "https://cdnjs.cloudflare.com/ajax/libs/pdf.js/3.11.174/pdf.min.js";
+    const WORKER_SRC = "https://cdnjs.cloudflare.com/ajax/libs/pdf.js/3.11.174/pdf.worker.min.js";
+
     const state = {
         pdfDoc: null,
         pdfBytes: null,
         lastViewport: null,
+        pdfJsReady: null,
     };
 
     function base64ToUint8(base64) {
@@ -32,17 +37,73 @@
 
     const pointerPads = new Map();
 
-    window.pdfInterop = {
+    function loadScriptOnce(url) {
-        ensureReady: () => {
+        return new Promise((resolve, reject) => {
-            if (pdfjsLib && pdfjsLib.GlobalWorkerOptions) {
+            // If already present, resolve immediately
-                // worker is already loaded via CDN include
+            const existing = Array.from(document.getElementsByTagName('script')).find(s => s.src === url);
+            if (existing && existing.dataset.loaded === "true") {
+                resolve();
                 return;
             }
+
+            const script = existing || document.createElement('script');
+            script.src = url;
+            script.defer = true;
+            script.onload = () => {
+                script.dataset.loaded = "true";
+                resolve();
+            };
+            script.onerror = (e) => reject(new Error(`Script load failed: ${url}`));
+
+            if (!existing) {
+                document.head.appendChild(script);
+            }
+        });
+    }
+
+    async function ensurePdfJsLoaded() {
+        if (typeof pdfjsLib !== "undefined") {
+            return;
+        }
+
+        if (!state.pdfJsReady) {
+            state.pdfJsReady = loadScriptOnce(PDF_JS_SRC);
+        }
+
+        await state.pdfJsReady;
+
+        if (typeof pdfjsLib === "undefined") {
+            throw new Error("pdfjsLib could not be loaded");
+        }
+    }
+
+    window.pdfInterop = {
+        ensureReady: async () => {
+            // Ensure pdf.js is present and the worker path is set explicitly.
+            await ensurePdfJsLoaded();
+            if (pdfjsLib && pdfjsLib.GlobalWorkerOptions) {
+                if (pdfjsLib.GlobalWorkerOptions.workerSrc !== WORKER_SRC) {
+                    pdfjsLib.GlobalWorkerOptions.workerSrc = WORKER_SRC;
+                }
+            } else {
+                throw new Error("pdf.js not available after load");
+            }
         },
         loadPdf: async (base64) => {
-            return await reloadFromBase64(base64);
+            await ensurePdfJsLoaded();
+            try {
+                const result = await reloadFromBase64(base64);
+                if (!result || !result.pages) {
+                    throw new Error("PDF has keine Seiten erkannt");
+                }
+                return result;
+            } catch (err) {
+                console.error("pdfInterop.loadPdf failed", err);
+                throw err;
+            }
         },
         renderPage: async (pageIndex, canvasId, targetWidth) => {
+            await ensurePdfJsLoaded();
             if (!state.pdfDoc) {
                 throw new Error('PDF not loaded');
             }
@@ -51,8 +112,14 @@
             const scale = targetWidth / rawViewport.width;
             const viewport = page.getViewport({ scale });
 
-            const canvas = document.getElementById(canvasId);
+            let canvas = document.getElementById(canvasId);
             if (!canvas) {
+                // give the UI a tiny delay to render the canvas into the DOM
+                await new Promise(r => setTimeout(r, 40));
+                canvas = document.getElementById(canvasId);
+            }
+            if (!canvas) {
+                console.error("renderPage: canvas not found", canvasId);
                 throw new Error('Canvas not found');
             }
             const ctx = canvas.getContext('2d');