Once upon a time, not all that long ago, Word, Excel, and PowerPoint were separate apps. Now the tools for creating, editing, and sharing files for all three document formats have been consolidated in a single Office app, along with a set of new PDF functions. (The app is free, of course, but unlocking most of its functionality requires a personal, business, or school account linked to a Microsoft 365 subscription.)
Although the formats are identical to those found on their desktop equivalents, the mobile app offers a few unique features. You can use the Lens button to snap a picture of a document and turn it into an editable PDF or Word file, for example, eliminating the need for the separate Microsoft Lens app, or transform a picture of a table on a printed page into a range in Excel. From the Actions tab, you can choose a PDF file and add your signature (using a finger or an Apple Pencil), and convert a PDF to a Word file or vice-versa. There's also an option to transfer files between a PC and your mobile device that works surprisingly well as long as the files are under the 30 MB size limit.
Office for iOS can connect to any cloud storage service that works directly with Office files, which includes Dropbox, Box, and Egnyte as well as a dozen or more smaller players. Google Drive is, alas, not supported.