Portable document format books are highly accepted and preferred ebooks. Pdf is the oldest format for the books and having the most use. There are many factors which are considered while selecting the pdf format as the best one among all such as • Free software to view pdf format book Readers can easily access these format books as for viewing such formatted books only there is a requirement of acrobat adobe reader which is available free of cost to download and install on web . • Table of content As by just setting the linking now it’s very easy to generate the table of contents for the book automatically. • Multilevel zoom options In the pdf format book multi level zooming options are available so it is very easy for the readers to zoom out the tiniest information that they needed such as contents written on the photos and maps. • Similar experience as the printed book Flipping options of the pdf book gives the same comfort and experience as the printed book offer to the readers. • Search options In the pdf format books there is also option for search anything by using the simple options. So it enables the readers to search easily the important keywords of the book. • Synchronized linking options In the pdf ebooks its very easy to give the references for the relevant and further detailed information through the links which gives the readers more synchronized information while reading particular book. • Cross platform accessibility Pdf format books have the cross platform accessibility as these books are independent of the hardware and operating system so the ebooks can be shared at any computer having different operating system. This feature of use all across the platform made these books the most preferred books • Digitally signed Pdf format books can be duly signed and the securely locked so these books can not be edited further which provide the security to publications for their copyrighted books from the editing for the wrong intentions. • Preserve originality Pdf format books retained the original quality and layout of the text of any book which has any kind of content, pictures, maps, audio, video and other graphics in it. So this feature helps to convey the mirror reflection of writer’s and publisher’s perception for the book to its end users • Scaling of information Due to feature of easy scaling of information these books are viewable similar on all kind of devices such as computer having large or small screen and mobile phones • Needs less storage space Pdf format e books occupy less storage space so that is why they are highly portable and easy to store • Annotation feature This feature makes these books more friendly as reader can highlight and take note while reading pdf format ebooks.