diff --git a/src/UglyToad.PdfPig.DocumentLayoutAnalysis/ReadingOrderDetector/ReadingOrderHelper.cs b/src/UglyToad.PdfPig.DocumentLayoutAnalysis/ReadingOrderDetector/ReadingOrderHelper.cs
new file mode 100644
index 00000000..04bf3d91
--- /dev/null
+++ b/src/UglyToad.PdfPig.DocumentLayoutAnalysis/ReadingOrderDetector/ReadingOrderHelper.cs
@@ -0,0 +1,163 @@
+namespace UglyToad.PdfPig.DocumentLayoutAnalysis.ReadingOrderDetector
+{
+    using System;
+    using System.Collections.Generic;
+    using System.Linq;
+    using UglyToad.PdfPig.Content;
+
+    /// <summary>
+    /// Helper functions for words and lines ordering.
+    /// </summary>
+    public static class ReadingOrderHelper
+    {
+        /// <summary>
+        /// Order words by reading order in a line.
+        /// <para>Assumes LtR and accounts for rotation.</para>
+        /// </summary>
+        /// <param name="words"></param>
+        public static List<Word> OrderByReadingOrder(this IEnumerable<Word> words)
+        {
+            if (words.Count() <= 1)
+            {
+                return words.ToList();
+            }
+
+            var TextOrientation = words.First().TextOrientation;
+            if (TextOrientation != TextOrientation.Other)
+            {
+                foreach (var word in words)
+                {
+                    if (word.TextOrientation != TextOrientation)
+                    {
+                        TextOrientation = TextOrientation.Other;
+                        break;
+                    }
+                }
+            }
+
+            switch (TextOrientation)
+            {
+                case TextOrientation.Horizontal:
+                    return words.OrderBy(w => w.BoundingBox.BottomLeft.X).ToList();
+
+                case TextOrientation.Rotate180:
+                    return words.OrderByDescending(w => w.BoundingBox.BottomLeft.X).ToList();
+
+                case TextOrientation.Rotate90:
+                    return words.OrderByDescending(w => w.BoundingBox.BottomLeft.Y).ToList();
+
+                case TextOrientation.Rotate270:
+                    return words.OrderBy(w => w.BoundingBox.BottomLeft.Y).ToList();
+
+                case TextOrientation.Other:
+                default:
+                    // We consider the words roughly have the same rotation.
+                    var avgAngle = words.Average(w => w.BoundingBox.Rotation);
+                    if (double.IsNaN(avgAngle))
+                    {
+                        throw new NotFiniteNumberException("OrderByReadingOrder: NaN bounding box rotation found when ordering words.", avgAngle);
+                    }
+
+                    if (0 < avgAngle && avgAngle <= 90)
+                    {
+                        // quadrant 1, 0 < θ < π/2
+                        return words.OrderBy(w => w.BoundingBox.BottomLeft.X).ThenBy(w => w.BoundingBox.BottomLeft.Y).ToList();
+                    }
+                    else if (90 < avgAngle && avgAngle <= 180)
+                    {
+                        // quadrant 2, π/2 < θ ≤ π
+                        return words.OrderByDescending(w => w.BoundingBox.BottomLeft.X).ThenBy(w => w.BoundingBox.BottomLeft.Y).ToList();
+                    }
+                    else if (-180 < avgAngle && avgAngle <= -90)
+                    {
+                        // quadrant 3, -π < θ < -π/2
+                        return words.OrderByDescending(w => w.BoundingBox.BottomLeft.X).ThenByDescending(w => w.BoundingBox.BottomLeft.Y).ToList();
+                    }
+                    else if (-90 < avgAngle && avgAngle <= 0)
+                    {
+                        // quadrant 4, -π/2 < θ < 0
+                        return words.OrderBy(w => w.BoundingBox.BottomLeft.X).ThenByDescending(w => w.BoundingBox.BottomLeft.Y).ToList();
+                    }
+                    else
+                    {
+                        throw new ArgumentException("OrderByReadingOrder: unknown bounding box rotation found when ordering words.", nameof(avgAngle));
+                    }
+            }
+        }
+
+        /// <summary>
+        /// Order lines by reading order in a block.
+        /// <para>Assumes TtB and accounts for rotation.</para>
+        /// </summary>
+        /// <param name="lines"></param>
+        public static IReadOnlyList<TextLine> OrderByReadingOrder(this IEnumerable<TextLine> lines)
+        {
+            if (lines.Count() <= 1)
+            {
+                return lines.ToList();
+            }
+
+            var TextOrientation = lines.First().TextOrientation;
+            if (TextOrientation != TextOrientation.Other)
+            {
+                foreach (var line in lines)
+                {
+                    if (line.TextOrientation != TextOrientation)
+                    {
+                        TextOrientation = TextOrientation.Other;
+                        break;
+                    }
+                }
+            }
+
+            switch (TextOrientation)
+            {
+                case TextOrientation.Horizontal:
+                    return lines.OrderByDescending(w => w.BoundingBox.BottomLeft.Y).ToList();
+
+                case TextOrientation.Rotate180:
+                    return lines.OrderBy(w => w.BoundingBox.BottomLeft.Y).ToList();
+
+                case TextOrientation.Rotate90:
+                    return lines.OrderByDescending(w => w.BoundingBox.BottomLeft.X).ToList();
+
+                case TextOrientation.Rotate270:
+                    return lines.OrderBy(w => w.BoundingBox.BottomLeft.X).ToList();
+
+                case TextOrientation.Other:
+                default:
+                    // We consider the lines roughly have the same rotation.
+                    var avgAngle = lines.Average(w => w.BoundingBox.Rotation);
+                    if (double.IsNaN(avgAngle))
+                    {
+                        throw new NotFiniteNumberException("OrderByReadingOrder: NaN bounding box rotation found when ordering lines.", avgAngle);
+                    }
+
+                    if (0 < avgAngle && avgAngle <= 90)
+                    {
+                        // quadrant 1, 0 < θ < π/2
+                        return lines.OrderByDescending(w => w.BoundingBox.BottomLeft.Y).ThenBy(w => w.BoundingBox.BottomLeft.X).ToList();
+                    }
+                    else if (90 < avgAngle && avgAngle <= 180)
+                    {
+                        // quadrant 2, π/2 < θ ≤ π
+                        return lines.OrderBy(w => w.BoundingBox.BottomLeft.X).ThenBy(w => w.BoundingBox.BottomLeft.Y).ToList();
+                    }
+                    else if (-180 < avgAngle && avgAngle <= -90)
+                    {
+                        // quadrant 3, -π < θ < -π/2
+                        return lines.OrderBy(w => w.BoundingBox.BottomLeft.Y).ThenByDescending(w => w.BoundingBox.BottomLeft.X).ToList();
+                    }
+                    else if (-90 < avgAngle && avgAngle <= 0)
+                    {
+                        // quadrant 4, -π/2 < θ < 0
+                        return lines.OrderByDescending(w => w.BoundingBox.BottomLeft.X).ThenByDescending(w => w.BoundingBox.BottomLeft.Y).ToList();
+                    }
+                    else
+                    {
+                        throw new ArgumentException("OrderByReadingOrder: unknown bounding box rotation found when ordering lines.", nameof(avgAngle));
+                    }
+            }
+        }
+    }
+}
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