diff --git a/Additional-Learning-Resources.md b/Additional-Learning-Resources.md
index ddd54c2..eeac24c 100644
--- a/Additional-Learning-Resources.md
+++ b/Additional-Learning-Resources.md
@@ -32,7 +32,7 @@ The PDF specification:
 + https://www.adobe.com/devnet/acrobat/pdfs/PDF32000_2008.pdf
 
 Presentations:
-+ http://labs.appligent.com/files/2013/03/recognizing_malformed_pdf_f.pdf
++ https://labs.appligent.com/files/2013/03/recognizing_malformed_pdf_f.pdf
 
 ## Examples
 
@@ -42,5 +42,5 @@ Presentations:
 ## Related projects
 
 Open source projects:
-+ http://poppler.freedesktop.org/
-+ http://www.mupdf.com/
\ No newline at end of file
++ https://poppler.freedesktop.org
++ https://www.mupdf.com
\ No newline at end of file