That is a great question. We would recommend if you are using Apple Pages on your Mac you may find it more beneficial to install Microsoft Office 365 om your Mac for future use. This will allow you to automatically save documents in a more usable format, one that will work on all the other computers you would use at school and elsewhere as well. In addition, you may find it easier to save it to your OneDrive for later access as well.
Here are two articles that will help get that set up:
(These apps are available for your phone/tablets too!)
But, what if you are using a friend's computer and you just need to convert from Pages?* Here is some information from Apple's own support page:
Pages for Mac: Export a Pages document to PDF or another file format*
You can export a Pages document to save a copy of it in another format—Microsoft Word, PDF, plain text (TXT), ePub, or Pages ‘09. Exporting a document is useful when you’re sharing it with others who may use different software from you. Any changes made to the exported document don’t affect the original.
Note: You can’t export page layout documents in ePub format.
Save a document in another format
Open the document, then choose File > Export To > [file format] (from the File menu at the top of your screen).
Specify export settings, which differ depending on the file type:
PDF: Choose an image quality. The higher the image quality, the larger the file size of the exported copy. To restrict access to the copy, select the “Require password to open” checkbox, then enter the requested information.
Word: To restrict access to the copy, select the “Require password to open” checkbox, then enter the requested information. If the file needs to be compatible with an older version of Word (1997-2004), click Advanced Options, then choose .doc from the pop-up menu.
ePub: Enter the title and author name. If you want to assign it to a category, click the Primary Category pop-up menu, then choose a category. To set the language and book cover and to set whether fonts are embedded, click the disclosure triangle next to Advanced Options.
Pages ‘09: To restrict access to the copy, select the “Require password to open” checkbox, then enter the requested information.
Click Next, then type a name for the document.
The filename extension (.pdf or .epub, for example) is automatically appended to the document name.
*The same process can be duplicated in all of Apple's "Works" Suite of Apps.
Want more information? Head to Apple's Support Page for Apple Apps.