Support for Microsoft's Office 2007 suite has come to an end this month, as per the planned obsolescence of the software. Microsoft tend to support their desktop applications for about 10 years, so this fits within that timeframe.
While "mainstream" support ended for Office 2007 some time ago, extended support was provided until this month. This means that while nothing new will have been added, any security issues will have been dealt with. With this support period now at an end, running any of the Office 2007 applications now poses a security risk to the machine, as all future problems will remain unpatched.
Also of note to anyone that uses Outlook 2007 to access email on an Office 365 account is that the method of email delivery is going to be changing in such a way that Outlook 2007 will no longer be able to access it as usual. There may be workarounds for this, but these will likely mean losing many features.
Anyone still using Office 2007 is advised to upgrade either a "boxed" version of Office 2016, or to move to their Office 365 service which provides ongoing access to whatever the latest version of Office happens to be at the time.
The next significant end of life date for Office is October 2020 when extended support expires for Office 2010. Mainstream support has already ended for this version.