A PDF reader is a software application that allows users to view, print, and annotate documents in the PDF (Portable Document Format). This format is widely used for sharing documents because it preserves the original layout, fonts, and images, making it ideal for reports, eBooks, and forms. Many PDF readers are available, ranging from free options like Adobe Acrobat Reader to paid versions with advanced features. Users can highlight text, add comments, and fill out forms, making PDF readers essential tools for both personal and professional use.