Final answer:
A workbook template generally has a .xlsx file extension, which is for Excel workbooks used for data organization and calculations.
Step-by-step explanation:
A workbook template typically uses the file extension .xlsx, which is associated with Microsoft Excel, a program often used for organizing data, performing calculations, and creating charts. This extension is for Excel workbooks, which can contain multiple sheets of data. The other extensions mentioned refer to different types of documents: .docx is used for Microsoft Word documents, .pptx for Microsoft PowerPoint presentations, and .pdf for Portable Document Format files, which are not editable without specific software.