If the file is Macro-Enabled then remove its Macro first and then add the file.
STEPS TO REMOVE THE MACRO ENABLED CONTENT
- Click on Enable Content
- Click on View menu in Menu bar and select Macro
- Select View Macros Option
- On the Macro popup window, select Marco and delete that.
- Now Go to File> Info> Convert
- Save as the file now, it will display a popup. Click on Yes
Now, file will be saved in Macro Free document.
You can use it now for signing the file.