Adds a couple of tests showing operations with the library

tests/QPdfSharp.Tests/QPdfExamplesTests.cs

@@ -0,0 +1,36 @@
+// Copyright © Stephen (Sven) Vernyi and Contributors. Licensed under the MIT License (MIT). See License.md in the repository root for more information.
+
+using QPdfSharp.Options;
+
+namespace QPdfSharp.Tests;
+
+public class QPdfExamplesTests
+{
+    [Fact]
+    public void Can_read_optimize_write_pdf()
+    {
+        // Read PDF
+        using var qpdf = new QPdf(TestAssets.Grug);
+
+        // Write with optimizations
+        qpdf.WriteFile("optimized.pdf", new QPdfWriteOptions
+        {
+            CompressStreams = true,
+            Linearize = true
+        });
+    }
+
+    [Fact]
+    public void Can_add_watermark_page_to_pdf()
+    {
+        // This watermark could be safely cached in memory with a long-held reference to QPdf.
+        using var watermark = new QPdf(TestAssets.QPdfWatermark);
+        using var qpdf = new QPdf(TestAssets.Grug);
+
+        // Prepend watermark page
+        qpdf.PrependPage(watermark.GetPage(0));
+
+        // Write PDF
+        qpdf.WriteFile("watermarked.pdf");
+    }
+}

tests/QPdfSharp.Tests/TestAssets.cs

@@ -6,4 +6,5 @@ public static class TestAssets
 {
     public const string Grug = "Assets/grug.pdf";
     public const string GrugJson = "Assets/grug.json";
+    public const string QPdfWatermark = "Assets/watermark.pdf";
 }