The file format commonly used to preserve the layout of documents across different systems is PDF (Portable Document Format). PDF files maintain the original formatting, fonts, and images regardless of the software or operating system used to view them. This universality makes PDFs ideal for sharing documents like reports, invoices, and eBooks, ensuring that they appear consistently to all users. Additionally, PDF files can be secured with passwords, encrypted, or compressed, enhancing their flexibility in various professional and personal applications.