diff --git a/src/UglyToad.PdfPig.Core/UglyToad.PdfPig.Core.csproj b/src/UglyToad.PdfPig.Core/UglyToad.PdfPig.Core.csproj
index 4b0a23c5e..51cac1a1e 100644
--- a/src/UglyToad.PdfPig.Core/UglyToad.PdfPig.Core.csproj
+++ b/src/UglyToad.PdfPig.Core/UglyToad.PdfPig.Core.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net462;net471;net6.0;net8.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net462;net471;net6.0;net8.0;net9.0</TargetFrameworks>
     <LangVersion>12</LangVersion>
     <Version>0.1.12-alpha001</Version>
     <IsTestProject>False</IsTestProject>
diff --git a/src/UglyToad.PdfPig.DocumentLayoutAnalysis/PageSegmenter/DocstrumBoundingBoxes.cs b/src/UglyToad.PdfPig.DocumentLayoutAnalysis/PageSegmenter/DocstrumBoundingBoxes.cs
index f07dcbd1b..56bbef6eb 100644
--- a/src/UglyToad.PdfPig.DocumentLayoutAnalysis/PageSegmenter/DocstrumBoundingBoxes.cs
+++ b/src/UglyToad.PdfPig.DocumentLayoutAnalysis/PageSegmenter/DocstrumBoundingBoxes.cs
@@ -48,12 +48,19 @@ public DocstrumBoundingBoxes(DocstrumBoundingBoxesOptions options)
         /// <returns>The <see cref="TextBlock"/>s generated by the document spectrum method.</returns>
         public IReadOnlyList<TextBlock> GetBlocks(IEnumerable<Word> words)
         {
-            if (words?.Any() != true)
+            if (words is null)
             {
                 return Array.Empty<TextBlock>();
             }
 
-            return GetBlocks(words.ToList(),
+            // Avoid multiple enumeration and unnecessary ToArray() if already a list
+            var wordList = words as IReadOnlyList<Word> ?? words.ToArray();
+            if (wordList.Count == 0)
+            {
+                return Array.Empty<TextBlock>();
+            }
+
+            return GetBlocks(wordList,
                 options.WithinLineBounds, options.WithinLineMultiplier, options.WithinLineBinSize,
                 options.BetweenLineBounds, options.BetweenLineMultiplier, options.BetweenLineBinSize,
                 options.AngularDifferenceBounds,
diff --git a/src/UglyToad.PdfPig.DocumentLayoutAnalysis/UglyToad.PdfPig.DocumentLayoutAnalysis.csproj b/src/UglyToad.PdfPig.DocumentLayoutAnalysis/UglyToad.PdfPig.DocumentLayoutAnalysis.csproj
index 1a750f4cf..6878b7e1e 100644
--- a/src/UglyToad.PdfPig.DocumentLayoutAnalysis/UglyToad.PdfPig.DocumentLayoutAnalysis.csproj
+++ b/src/UglyToad.PdfPig.DocumentLayoutAnalysis/UglyToad.PdfPig.DocumentLayoutAnalysis.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net462;net471;net6.0;net8.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net462;net471;net6.0;net8.0;net9.0</TargetFrameworks>
     <LangVersion>12</LangVersion>
     <Version>0.1.12-alpha001</Version>
     <IsTestProject>False</IsTestProject>
diff --git a/src/UglyToad.PdfPig.DocumentLayoutAnalysis/WordExtractor/NearestNeighbourWordExtractor.cs b/src/UglyToad.PdfPig.DocumentLayoutAnalysis/WordExtractor/NearestNeighbourWordExtractor.cs
index d5c48b208..4e0ce710c 100644
--- a/src/UglyToad.PdfPig.DocumentLayoutAnalysis/WordExtractor/NearestNeighbourWordExtractor.cs
+++ b/src/UglyToad.PdfPig.DocumentLayoutAnalysis/WordExtractor/NearestNeighbourWordExtractor.cs
@@ -51,34 +51,49 @@ public IEnumerable<Word> GetWords(IReadOnlyList<Letter> letters)
 
             if (options.GroupByOrientation)
             {
-                // axis aligned
-                List<Word> words = GetWords(
-                    letters.Where(l => l.TextOrientation == TextOrientation.Horizontal).ToList(),
-                    options.MaximumDistance, options.DistanceMeasureAA, options.FilterPivot,
-                    options.Filter, options.MaxDegreeOfParallelism);
-
-                words.AddRange(GetWords(
-                    letters.Where(l => l.TextOrientation == TextOrientation.Rotate270).ToList(),
-                    options.MaximumDistance, options.DistanceMeasureAA, options.FilterPivot,
-                    options.Filter, options.MaxDegreeOfParallelism));
+                var buckets = new List<Letter>[5];
+                for (int i = 0; i < buckets.Length; i++) buckets[i] = new List<Letter>();
 
-                words.AddRange(GetWords(
-                    letters.Where(l => l.TextOrientation == TextOrientation.Rotate180).ToList(),
-                    options.MaximumDistance, options.DistanceMeasureAA, options.FilterPivot,
-                    options.Filter, options.MaxDegreeOfParallelism));
-
-                words.AddRange(GetWords(
-                    letters.Where(l => l.TextOrientation == TextOrientation.Rotate90).ToList(),
-                    options.MaximumDistance, options.DistanceMeasureAA, options.FilterPivot,
-                    options.Filter, options.MaxDegreeOfParallelism));
+                foreach (var l in letters)
+                {
+                    switch (l.TextOrientation)
+                    {
+                        case TextOrientation.Horizontal: buckets[0].Add(l); break;
+                        case TextOrientation.Rotate270: buckets[1].Add(l); break;
+                        case TextOrientation.Rotate180: buckets[2].Add(l); break;
+                        case TextOrientation.Rotate90: buckets[3].Add(l); break;
+                        default: buckets[4].Add(l); break;
+                    }
+                }
 
-                // not axis aligned
-                words.AddRange(GetWords(
-                    letters.Where(l => l.TextOrientation == TextOrientation.Other).ToList(),
-                    options.MaximumDistance, options.DistanceMeasure, options.FilterPivot,
-                    options.Filter, options.MaxDegreeOfParallelism));
+                // Use a thread-safe collection to avoid lock contention.
+                var results = new List<Word>(letters.Count); // Pre-allocate for performance
 
-                return words;
+                // Limit parallelism to avoid oversubscription.
+                var parallelOptions = new System.Threading.Tasks.ParallelOptions
+                {
+                    MaxDegreeOfParallelism = options.MaxDegreeOfParallelism > 0 ? options.MaxDegreeOfParallelism : Environment.ProcessorCount
+                };
+
+                // Use partitioner for better load balancing and avoid ConcurrentBag overhead
+                System.Threading.Tasks.Parallel.ForEach(
+                    System.Collections.Concurrent.Partitioner.Create(0, buckets.Length),
+                    parallelOptions,
+                    range =>
+                    {
+                        for (int i = range.Item1; i < range.Item2; i++)
+                        {
+                            if (buckets[i].Count == 0) continue;
+                            var measure = (i == 4) ? options.DistanceMeasure : options.DistanceMeasureAA;
+                            var words = GetWords(buckets[i], options.MaximumDistance, measure, options.FilterPivot, options.Filter, options.MaxDegreeOfParallelism);
+                            lock (results)
+                            {
+                                results.AddRange(words);
+                            }
+                        }
+                    });
+                results.TrimExcess();
+                return results;
             }
             else
             {
diff --git a/src/UglyToad.PdfPig.Fonts/UglyToad.PdfPig.Fonts.csproj b/src/UglyToad.PdfPig.Fonts/UglyToad.PdfPig.Fonts.csproj
index 8c8b2075e..774c47c28 100644
--- a/src/UglyToad.PdfPig.Fonts/UglyToad.PdfPig.Fonts.csproj
+++ b/src/UglyToad.PdfPig.Fonts/UglyToad.PdfPig.Fonts.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net462;net471;net6.0;net8.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net462;net471;net6.0;net8.0;net9.0</TargetFrameworks>
     <LangVersion>12</LangVersion>
     <Version>0.1.12-alpha001</Version>
     <IsTestProject>False</IsTestProject>
diff --git a/src/UglyToad.PdfPig.Tests/UglyToad.PdfPig.Tests.csproj b/src/UglyToad.PdfPig.Tests/UglyToad.PdfPig.Tests.csproj
index 2d8aff568..e3e298c8c 100644
--- a/src/UglyToad.PdfPig.Tests/UglyToad.PdfPig.Tests.csproj
+++ b/src/UglyToad.PdfPig.Tests/UglyToad.PdfPig.Tests.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>net471;net8.0</TargetFrameworks>
+    <TargetFrameworks>net471;net8.0;net9.0</TargetFrameworks>
     <IsTestProject>true</IsTestProject>
     <IsPackable>false</IsPackable>
     <DebugType>full</DebugType>
diff --git a/src/UglyToad.PdfPig.Tokenization/UglyToad.PdfPig.Tokenization.csproj b/src/UglyToad.PdfPig.Tokenization/UglyToad.PdfPig.Tokenization.csproj
index 88731a0b3..2f3e0d293 100644
--- a/src/UglyToad.PdfPig.Tokenization/UglyToad.PdfPig.Tokenization.csproj
+++ b/src/UglyToad.PdfPig.Tokenization/UglyToad.PdfPig.Tokenization.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net462;net471;net6.0;net8.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net462;net471;net6.0;net8.0;net9.0</TargetFrameworks>
     <LangVersion>12</LangVersion>
     <Version>0.1.12-alpha001</Version>
     <IsTestProject>False</IsTestProject>
diff --git a/src/UglyToad.PdfPig.Tokens/UglyToad.PdfPig.Tokens.csproj b/src/UglyToad.PdfPig.Tokens/UglyToad.PdfPig.Tokens.csproj
index 4c95062f3..069167812 100644
--- a/src/UglyToad.PdfPig.Tokens/UglyToad.PdfPig.Tokens.csproj
+++ b/src/UglyToad.PdfPig.Tokens/UglyToad.PdfPig.Tokens.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net462;net471;net6.0;net8.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net462;net471;net6.0;net8.0;net9.0</TargetFrameworks>
     <LangVersion>12</LangVersion>
     <Version>0.1.12-alpha001</Version>
     <IsTestProject>False</IsTestProject>
diff --git a/src/UglyToad.PdfPig/UglyToad.PdfPig.csproj b/src/UglyToad.PdfPig/UglyToad.PdfPig.csproj
index 2fb282e6e..797c83107 100644
--- a/src/UglyToad.PdfPig/UglyToad.PdfPig.csproj
+++ b/src/UglyToad.PdfPig/UglyToad.PdfPig.csproj
@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net462;net471;net6.0;net8.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net462;net471;net6.0;net8.0;net9.0</TargetFrameworks>
     <LangVersion>12</LangVersion>
     <Version>0.1.12-alpha001</Version>
     <IsTestProject>False</IsTestProject>