Cannot activate WP-Document Revisions

I installed Link Manager and the document revisions plugins according to the instructions provided in the respective ReadMes file that only mentioned copying the contents of the download to the/var/www/wordpress/WP-Contentss/Plugins folder which I did. When I tried to follow the second part of the instruction to enable the new plugs in in the dashboard of the server I could not see either of the new plugins listed. I remembered that WordPress frequently exclude from their instruction advice about what permissions need to be set on the copied files so I changed the owner to www-data like the other functioning plugins. Now I was able to see both plugins and activate the Link Manager however when I tried to activate Document Revisions I got the following error.

“Warning: include(/var/www/wordpress/wp-content/plugins/wp-document-revisions/includes/front-end.php): failed to open stream: Permission denied in /var/www/wordpress/wp-content/plugins/wp-document-revisions/wp-document-revisions.php on line 106 Warning: include(): Failed opening ‘/var/www/wordpress/wp-content/plugins/wp-document-revisions/includes/front-end.php’ for inclusion (include_path=’.:/usr/share/php:/usr/share/pear’) in /var/www/wordpress/wp-content/plugins/wp-document-revisions/wp-document-revisions.php on line 106 Fatal error: Class ‘Document_Revisions_Front_End’ not found in /var/www/wordpress/wp-content/plugins/wp-document-revisions/wp-document-revisions.php on line 107.”
What do I need to do next to get this to work?