Error when I try to attach a document to an bill or invoice.

I just found this article on Accountex, a very good source of qb info.  At the bottom, it says office 2016 is not compatible with qb.  The article is older, so I am not sure if that is the issue.  Basically, this is what it says:

Intuit’s system requirements websites don’t list any version of QuickBooks as being compatible with Microsoft Office 2016 at this time, even the recently released QuickBooks 2016 product. That isn’t surprising, as Intuit usually starts final testing with any new Microsoft product after the public release (since Microsoft tends to make changes right up to the last moment). It can take time for them to make adjustments. 

My recommendation is that unless there is a strong reason for you to move up to Office 2016, don’t rush into it now if you are using QuickBooks. If you need to, though, everything should work fine other than Microsoft Outlook, in general as long as you have up-to-date software (including QuickBooks 2016). If you have older software, you may have problems. Looking at specific versions of QuickBooks:

QuickBooks 2016: Everything should work other than although you might have problems with Microsoft Outlook.
QuickBooks 2015: Everything should work (other than although you may have trouble with Microsoft Outlook), but you will need to patch your system if you want to use QuickBooks Statement Writer.

So perhaps it is fixed by now.  Every article on the help/support area I could find had dead links.  I would try going to help>update qb and do a full update and see if that helps.