There is an issue with a new feature of the Security Centre in the Windows 10 Fall Creators Update It's the "Controled Folder Access" which blocks 'Unauthorised' programmes from making changes to certain folders. This is an anti-ransomware feature to help prevent your data files from being encrypted by ransomware. The folders protected by default are your- Documents, Pictures, Videos, Music, Favourites, and your Desktop folders. You can add other folders to the protection list. However Controlled Folder Access works on a "block everything by default" basis. Of course Microsoft's own software is allowed through by default. So for example if you use a 3rd party Text editor you may find that it suddenly cannot save to your Documents folder. Any 3rd party programme/application that tries to save to, or delete something from, one of the protected folders may be blocked. (And if you have turned off Defender notifications you will be scratching your head as to why). It's not clear yet just how many 3rd party programmes this affects, it seems that some are affected some are not. eg. Softmaker FreeOffice is affected, Irfanview isn't. If you find you suddenly can't save a file because of this then try saving to the OneDrive folder, this is not in the protected list by default. There are 2 ways to fix the problem. You can turn off Controled Folder Access altogether.[/*] You can make the 3rd party programme you use an exception in the Controled Folder Access.[/*] To allow a programme through the Controled Folder Access: Open the Security Centre and go to Virus & Threat Protection > Virus & threat protection settings > Allow an app through controlled folder access > +add an allowed app. Browse to the .exe file of the app you want to allow, select it and click Open.