If you want to scan a document to PDF using Windows Scan app, then set the File type to PDF, and press the Scan button to get the output. Or else, if you are using another scanner app then first scan your document and when the scanned pages are added on the app interface, use the Print option in the File menu. When the Print box is opened, select Microsoft Print to PDF option as your printer, adjust the print settings, and hit the Print button.