change pdf -> PDF

Author: ankitsmt211

application/src/main/java/org/togetherjava/tjbot/features/help/HelpThreadAutoArchiver.java

@@ -99,7 +99,7 @@ private void autoArchiveForThread(ThreadChannel threadChannel, Instant archiveAf
 
                                 Also try to make the information **easily accessible** by sharing code
                                 or assignment descriptions directly on Discord, not behind a link or
-                                pdf file; provide some guidance for long code snippets and ensure
+                                PDF-file; provide some guidance for long code snippets and ensure
                                 the **code is well formatted** and has syntax highlighting. Kindly read through
                                 %s for more.