doc
Files with .doc extension represent documents generated by Microsoft Word or other word processing documents in binary file format.
The extension was initially used for plain text documentation on several different operating systems.
It can contain several different types of data such as images, formatted as well as plain text, graphs, charts, embedded objects, links, pages, page formatting, print settings and a lot others.
The format was popular for all sorts of documentation due to the variety of options it offers to users for writing manuals, proposals, specifications, resumes, articles or any similar documents.
The updated version of DOC is DOCX which is based on Office OpenXML whose specifications are openly available.
pdf
Portable Document Format (PDF) is a type of document created by Adobe back in 1990s.
The purpose of this file format was to introduce a standard for representation of documents and other reference material in a format that is independent of application software, hardware as well as Operating System.
The PDF file format has full capability to contain information like text, images, hyperlinks, form-fields, rich media, digital signatures, attachments, metadata, Geospatial features and 3D objects in it that can become as part of source document.
In most of the cases, existing documents are converted to PDF rather than creating a new PDF from scratch.
But that doesn’t mean there are no software for creation or manipulation of PDF files.