feat: add password support for encrypted PDFs (Phase 5.2)

- Add Password property to PdfSource base class
- Android: Use .password() configurator to unlock encrypted PDFs
- iOS: Use PdfDocument.Unlock() and IsLocked property
- Handle password errors gracefully on both platforms
- Throw error if PDF is locked but no password provided
- Throw error if provided password is incorrect
- Cross-platform password-protected PDF support complete

Author: michaelstonis

src/MauiNativePdfView/Abstractions/PdfSource.cs

@@ -5,6 +5,12 @@ namespace MauiNativePdfView.Abstractions;
 /// </summary>
 public abstract class PdfSource
 {
+    /// <summary>
+    /// Gets or sets the password for encrypted PDF documents.
+    /// Leave null or empty for non-encrypted PDFs.
+    /// </summary>
+    public string? Password { get; set; }
+
     /// <summary>
     /// Creates a PDF source from a file path.
     /// </summary>

src/MauiNativePdfView/Platforms/Android/PdfViewAndroid.cs

@@ -271,6 +271,12 @@ private void ConfigureAndLoad(PDFView.Configurator configurator, int pageToResto
         bool enablePageSnap = _displayMode == Abstractions.PdfDisplayMode.SinglePage;
         bool enablePageFling = _displayMode == Abstractions.PdfDisplayMode.SinglePage;
 
+        // Set password if provided
+        if (!string.IsNullOrEmpty(_source?.Password))
+        {
+            configurator.Password(_source.Password);
+        }
+
         configurator
             .EnableSwipe(_enableSwipe)
             .EnableDoubleTap(_enableZoom)

src/MauiNativePdfView/Platforms/iOS/PdfViewiOS.cs

@@ -292,6 +292,25 @@ private void LoadDocument()
 
             if (document != null)
             {
+                // Check if document is locked and attempt to unlock with password
+                if (document.IsLocked)
+                {
+                    if (!string.IsNullOrEmpty(_source.Password))
+                    {
+                        bool unlocked = document.Unlock(_source.Password);
+                        if (!unlocked)
+                        {
+                            OnError(new PdfErrorEventArgs("Failed to unlock PDF: incorrect password"));
+                            return;
+                        }
+                    }
+                    else
+                    {
+                        OnError(new PdfErrorEventArgs("PDF is password-protected but no password was provided"));
+                        return;
+                    }
+                }
+
                 _pdfView.Document = document;
 
                 // Get document metadata
@@ -355,6 +374,11 @@ private void OnPageChangedNotification(NSNotification notification)
         }
     }
 
+    private void OnError(PdfErrorEventArgs args)
+    {
+        Error?.Invoke(this, args);
+    }
+
     private void HandleTap(UITapGestureRecognizer recognizer)
     {
         var location = recognizer.LocationInView(_pdfView);