By default, Pages saves your document as a single file. If your document is over 500 MB or contains large video or image files, Pages may perform better if you save the document as a package.
Save as a package file: Click anywhere in the document window to make it active, then choose File > Advanced > Change File Type > Package (from the File menu at the top of your screen).
Revert a package file to single-file format: Choose File > Advanced > Change File Type > Single File. You may need to revert because some web or email services don’t allow you to upload or attach a package file.
See the Apple Support article Save documents as a package or a single file for more information.