Currently, we are using hard code text in the alert. You can follow below steps to change the content of the message
1. Create folder: root -> templates -> your_using_template -> html -> mod_edocman_search
2. Copy file: root -> modules -> mod_edocman_search -> tmpl -> default.php into that folder
3. Open that file by notepad and change content of the message:
"Please enter keyword for searching"