By default, Pages saves your document as a single file. If your document is very large or has a lot of movie or image files, you may want to save it as a package file.
You can change a package file to a single-file format to improve the performance of Pages. Some web or email services don’t allow you to upload or attach a package file.
Choose File > Advanced > Change File Type > Package (or Single File).
See this Apple Support article for more information.