Portable Document Format (PDF) was created by Adobe to present and exchange documents reliably - independent of software, hardware, or operating system.

The PDF is an open standard, maintained by the International Organization for Standardization (ISO). PDF documents can contain links and buttons, form fields, audio, video, and business logic. They can be signed electronically, and you can easily view PDF files on Windows or Mac OS using the free Acrobat Reader software.

There are multiple types of PDF:

Word processer and save as PDFs - Digitally created PDFs are made by directly saving a document being drafted in a word processor (like Microsoft Word) as a PDF

Image-based PDFs - Image-only PDFs are created through scanning, taking photographs, or taking screenshots. These documents are “locked” in a snapshot type image and are not searchable, cannot be copied and pasted, and cannot be marked up.

OCR’ed or “made-searchable” PDFs - Image-based text PDFs can be made text-searchable via the application of optical character recognition (OCR). During the OCR process, characters and the document structure are “read.” As a result, a text layer is added to the image layer. Depending on the quality of the image, or the readability of the writing, may not be 100% accurate.