What is the pdf format in adobe acrobat? And why do we use this format to save Documents ?

Actually PDF files are editable using some software like adobe distiller. However, the main objective of using the PDF file system is that it is a cross platform, OPERATING SYSTEM OR PLATFORM INDEPENDENT therefore you can use it from almost all operating systems. That is why it is called an Universal format.

 

PDF means Portable Document Format, from it's name, u can learn one of its advantages is Portable.

 

Some advantages of PDF format:

(1) Portable

for the moment, u can read a PDF document in a wide range of devices, such as, PC, Mac, iPhone, BlackBerry, Kindle, etc.

(2) Security

u can set owner password and user password to protect ur PDF document. u can also set permissions to disable printing, disable copying, disable modifying for a PDF document.

(3) PDF always keeps the same page layout when u view it on different OS platform.

Portable Document Format In addition to above extractions from Wikipedia, this was developed by adobe Systems.
http://en.wikipedia.org/wiki/Portable_Document_Format

In my own point. we create a file and save as pdf as protected data and read it in adobe reader. We use Adobe Acrobat to open and edit the file that save as pdf so only adobe acrobat can re-edit the pdf file. and Adobe Acrobat is very useful software to creat a data a portfolio or save a file as .word, .xlx or powerpoint.. 

Portable Document Format (PDF) is a file format used to represent documents in a manner independent of application software, hardware, and operating systems.Each PDF file encapsulates a complete description of a fixed-layout flat document, including the text, fonts, graphics, and other information needed to display it.
In 1991, Adobe Systems co-founder John Warnock outlined a system called "Camelot"that evolved into PDF.

Portable Document Format (PDF), it is used to avoid confusion among versions, as Docx file can't be opened in MS office 2003.
for drawing, sketches, executable file may required the primary software which could be cost effect and time consuming as well.
Acrobat Reader and Foxit are usually available on every PC so in that we use this kind of format which should be accessible to everyone.
Beside, PDF is also used for prohibiting edit the original document.

Simple Answer .
PDF - and simply it makes the Documents to be read Easily and makes them Protected from any mistaken clicks or typing when reading .

It is secure,it is universally accepted file system and keeps a uniform layout when opening it .

PDF formats allow professionals to edit, share, collaborate and ensure the security of the content within digital documents. it's easily portable that's why its called Portable Document Format.

and its very light in size and displays excellent result in Vector and Raster documents, The content is not distorted in PDF .