When working in InDesign, always save as an InDesign Document (.indd). This allows changes to be made to the document in the future. If the project is only saved as a PDF, it will be very difficult or outright impossible to edit it later. Work from an InDesign Document file and export, such as to a PDF, when done.

To save as an InDesign Document, navigate to File > Save.

To export the document as a high-quality PDF, navigate to File > Adobe PDF Presets > High Quality Print. This is the best option for printing from a regular printer. 

To export the project as a different file format, such as an image or an HTML document, navigate to File > Export and select the desired file type in the Format drop-down. If saving as an image, JPEG is recommended for projects with any photos, and PNG for projects with just text and shapes.

In order to transport or share projects, the document must be packaged. Packaging will bundle the InDesign document along with any relevant assets, such as linked images and fonts. Packaging will ensure that everything required for the document to display correctly is included. Additionally, if the document is going to be professionally printed, the print shop may ask for the document to submitted as a package.