diff --git a/setup.cfg b/setup.cfg
index 28680a7..ff06662 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -40,9 +40,11 @@ python_requires = >=3.6
 
 install_requires =
     importlib-metadata; python_version<"3.8"
-    python-pdfbox>=0.1.8.1
+    # Read and write bookmarks from PDF
     PyPDF2>=1.26.0
+    # Read the input file and convert it to HTML
     Markdown>=3.3.4
+    # Parse the HTML to generate bookmarks
     html5>=0.0.9