You “can” use something else, like LibreOffice. However, in my experience, Microsoft Office is far better.
If you intend to use it for personal use, LibreOffice is absolutely fine. Should you decide to use it for business use, then you’ll soon start noticing that the documents produced by LibreOffice when exporting to OOXML (Microsoft’s format and, de-facto, the most common) are far from identical especially when it comes to PowerPoint and your slideshows will look very different and often awful once opened with Microsoft Office (meaning: the receiving end).
Should you need it for professional use what I would do, if I were you, would be to give a try to Office 365 as it doesn’t cost much and also gives you 1TB of OneDrive. If you are happy with the software (and OneDrive) you keep it and keep paying the subscription, otherwise you stop paying and uninstall it.