In Microsoft Office products such as Word, Excel, Outlook or Publisher, the Recently used file list may be grayed out under Tools > Options > General. Here’s how to fix this.

1. Hold down the Windows key and press R (Or click Start > Run).

2. Type regedit and click OK.

3. Click the plus sign next to HKEY_CURRENT_USER
then Software
then Microsoft
then Windows
then CurrentVersion
then Policies
then click Explorer

4. Look for an entry on the right side for NoRecentDocsHistory. Right-click the entry and Delete it.

Now you should be able to access Recently used file list.

Source: “Recently used file list” grayed out on Word