It wouldn’t be a Microsoft platform without Office applications, and the usual suspects are all pre-installed. Office is a unified app on Windows Phone (8.1), though I believe that Word, Excel, and PowerPoint may be split out into individual apps on Windows 10.
Office natively provides access to documents on the phone’s internal and removable storage, in email attachments, and in your OneDrive or Office 365 account. You can organise them as you wish.
There’s also a dedicated OneDrive app, which is handy if you store a lot of stuff in Microsoft’s cloud. It’s a simple file-browser, with the ability to organise files as well as inspect them.
Word has a simple interface, with distinct viewing and editing modes, much like Pages on the iPhone.
A subset of all supported formatting options is presented in straightforward panels.
Excel is here too, complete with its trademark green livery.
Landscape mode is naturally supported.
PowerPoint is here too, but you can only open, view, and edit presentations on Windows Phone - not create them. You can make them in Office on a computer or in Office 365, and add them to OneDrive, though; then they’ll show up on your Windows Phone device.
PowerPoint supports presentation mode in landscape orientation, including external displays.
Settings for presenting on external displays live in the Settings app.