You can disable inline previews for files in the Rich Content Editor. The Rich Content Editor is used in features that support the editor (Announcements, Assignments, Discussions, Pages, Quizzes, or Syllabus).
Open Rich Content Editor
Open the Rich Content Editor using one of the Canvas features which support the Editor.
Locate Content Selector
The Content Selector will automatically open when the Rich Content Editor is opened.
Open URL Link Icon
Make sure the cursor is in the file link somewhere . Click the URL link icon  to open a popup window.
Disable Inline Preview
Click the Disable inline previews for this link checkbox . Then click on Update Link .
Click the Save button to save any changes to the post made in the Rich Content Editor.
Note: When using the Rich Content Editor in Assignments, Discussions, Pages, and Quizzes, you have the option to Save & Publish. When using the Rich Content Editor in the Syllabus and Discussions pages, the Save button may appear as “Update Syllabus” or “Post Reply”.
Once you disable the inline preview, the file can no longer can be previewed. Users will have to click the link to open the file.