You can configure the document's Security Settings to make the PDF read only.
1. Click Document > Security > Show Security Settings for this Document.
2. Select Security Method as Password Security.
3. At the Password Security Settings dialog, check the Permissions box and assign a Permissions password known only to you (users can open the document without knowing this password)
a. Define a setting for printing of the document as needed
b. Define the setting for changing the document (None=read only; other restrictions are possible—experiment!)
c. Enable copying of the document if needed
4. Click OK to save these settings.
5. Retype the Permissions password in Step 3.
6. You must save the document to preserve these settings.