There are over 20 million PDF Files on the web, and over half represent some kind of printable form - from insurance claims, mortgage applications, invoices, order forms, employment applications, and so on. With so many PDFs in circulation, have you ever wondered - what exactly is a PDF?

A PDF (or portable document file) is a universally-accepted file format for distributing electronic information. First developed by Adobe Corporation, PDFs have a.PDF file extension and are very portable between computer platforms. This means they can be created on a Mac, for example, uploaded to a UNIX-based website, then read or printed from a PC. Its versatility means PDF is now a published ISO standard.

The beauty of a PDF is that it allows the saving or distribution of pages with a high degree of design content, without losing any of the original layout. The effect is that a PDF feels much more like a viewing a paper document. This is one of the primary reasons why the format has become so universally popular.

Another is that a PDF is indexable – that is, PDFs can contain links to different parts of the document, which makes them ideal for electronic catalogues or reports that contain an index.

Anyone can create applications that can read and write PDF files without having to pay royalties. Although Adobe Systems holds the patents, it licenses them for royalty-free use in software development.

PDF documents can be created using a number of publishing programs, usually with the aid of an add-on. There are also programs that will add PDF creation as a printer option on your computer. Any documents sent to Print with the PDF printer driver selected are converted into a PDF file.

Yet, despite the proliferation of PDF publishing software, the main program for creating PDFs remains Adobe Acrobat Distiller.

However, the versatility and popularity of the PDF format has created one particular problem, and that is the huge diversity in the way a PDF form can be created.

Although Adobe Reader is able to create editable PDF forms, not all programs are equipped to do so. Some PDF forms, for instance, are created by scanning a hardcopy print into a computer, and the image then converted into a PDF. In such cases, the PDF form is not editable by Adobe Reader, leaving the user little alternative other than to print the form back to a hardcopy and fill it in by hand. The only other choice is to re-design the form from scratch, making sure the output PDF is editable.

But what happens if there are many PDF forms – perhaps as part of an extensive archive - and the task of re-designing from scratch is impractical?

There are, thankfully, a few solutions that will enable you to fill in and print PDF forms that can't be filled in using Adobe Reader. You just need to search of “PDF Form Filler’ in Google to see how many solutions are available.

For anyone wanting to edit a non-editable PDF, there are plenty of choices available. There are solutions that let you fill PDF Forms on-line, by first uploading it to a website, editing it online, and then printing, emailing, faxing or exporting it. However, many of these sites usually require the user to register first, or to open a subscriber account, or make some for form of charge. Others limit the ‘free’ features until the user has registered at the very least.

However, not all solutions are of the ‘nothing for nothing’ variety; there are a small number that do actually offer ‘something for nothing’.

One such program is the Blueberry PDF Form Filler, which is a small, easy-to-use desktop program that is completely free to download and use.

The Blueberry PDF Form Filler enables users to fill in PDF forms regardless of what format they're in - even PDFs that can't be filled in using Adobe Reader.