Hi,

I may suggest you hide the section using the CSS code below: 

#wpforo #wpforo-wrap .wpforo-messages-content .wpf_attach_button_wrap {display:none;}

The CSS code should be inserted in the "Custom CSS code" textarea of the "Colors & Styles" tab within the wpForo Settings page. 

Please note: all questions related to paid addons should be asked in the gVectors.com forum. Here, we only support issues related to the free wpForo plugin.

For support regarding the wpForo Private Messages addon, please visit the dedicated forum: https://gvectors.com/forum/wpforo-private-messages/