PDF (Portable Document Format) is a common choice for e-books, big manuals comprising of several hundred pages and other documents. At a first glance, it seems to be a reasonable choice. PDF is a really cross-platform format, the most popular PDF viewer – Adobe Acrobat – is freely available in all popular operating systems – Windows, Mac OS and Linux. But what is wrong with it?

Well, the first of all, it tends to be slow, of course, it might depend on an application you are viewing your document with, but still opening large files in Adobe Acrobat doesn’t seem to be an easy walk. Of course, it’s not the only reason why I think this format is a poor choice for e-books.

There is a significant disadvantage of PDF – its searching capabilities. Frankly speaking, it’s not format’s fault, but a glitch of the current PDF viewers. The problem with searching through PDF is its linearity, I mean, when finding some word or a phrase it will show you every occurrence of that word or phrase from the top of the document to its bottom. Sure, you can open the “Full Reader Search” window, but still it will just represent a list of matched occurrences.  So, it’s not very convenient to search through a 500 pages document for a word that you might find in its bottom or in the middle of the document.

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Nevertheless, there is a document word that doesn’t have the above mentioned disadvantages. I suppose everyone must be familiar with it. It’s CHM (Microsoft HTML Help). In fact, the format is just a collection of simple HTML pages. But unlike PDF, CHM is quite fast. It supports chapters, yes, PDF does also can contain chapters in the document, but they are no so convenient. In addition, when you open a PDF document, all its contents get loaded at once, while CHM only loads the pages and the chapters you are reading.

And of course the main advantage of CHM over PDF is its search capabilities. When you search through a CHM documents you will get a list of the relevant chapters and pages ordered by their relevancy.  The CHM search engine is also morphological a ware.

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In a conclusion I’m going to say that actually it’s quite obvious that PDF is such common as an e-book format because it is the format that is used for submitting books to a printing office and therefore they don’t have to prepare any other kind of documents to publish an e-book, they can just sell PDFs, while creating a CHM file involves a greater amount of work. As a result such e-books don’t have any significant advantages over printed ones. Sure, they don’t take any space on a bookshelf, they are cheaper than paper books and they don’t require cutting wood to create paper, but still they are not very convenient for reading and finding some information.

Anyway, there are some places on the Net where it is possible to find CHM e-books.