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What is a CHM File and How to Convert it to PDF Format?

What is a CHM File and How to Convert it to PDF Format?

Microsoft's proprietary format for Help files, which has also been the leading preference for such files since the late 90s, may be perfect for Help resource documents, but other files of the same CHM format are not as convenient to access, owing to the format's many limitations. Techspirited describes the CHM standard in detail, and lists out the ways in which CHM files can be converted to the widely accepted PDF format.
Padmini Krishna
Did You Know?
Since Windows 98, when the CHM format made its first appearance, a handful of newer versions of Windows along with their service packs have been released. Each version handles CHM files differently, and hence sometimes, invariably, it may not be possible for some computers to open certain CHM files. This problem, however, can be worked around by opening the file's "Properties" window and unblocking the file.

It is not possible to be a frequent computer, laptop, or even smartphone user, and not have heard about the PDF file format. PDF is an acronym for Portable Document Format, and files of this format have been in circulation since 1993. Although PDF was originally an Adobe proprietary format, it has recently been published as an open standard. It is one of the most commonly used formats today for the creation of almost any document-based media.

The Microsoft Compiled HTML Help (CHM) file format, on the other hand, is not as universal. Although the ideal choice of format while designing a file that contains Help topics is CHM, it has a number of limitations; not to mention, in certain circumstances. Windows refuses to allow you to open files of this format altogether! In these cases and of course for many other reasons, one may wish that they could access the document in question in a different and more widespread format such as PDF.

Below, we have provided a detailed description of the CHM file format, and also suggestions regarding how to convert files of this format to the PDF format.

Everything There is to Know About the CHM File Format
The Compiled HTML Help file format was introduced along with the release of Microsoft Windows 98, and it was made the primary standard for Windows Help file, a role that was previously fulfilled by Microsoft WinHelp.

Structure of a Typical .CHM File
Files of this format are essentially a collection of HTML pages, compressed and presented as binary files.

Apart from text, these files sometimes contain images and/or Javascript objects. Links to external pages may also be present.

Files of this format are equipped with complete in-file navigation support, including full text search.

The document, in general, has a tree structure, complete with an index page that contains hyperlinks to various sections.

Key Features and Benefits
Since a CHM file contains pages that are written in HTML, any conventional Internet browser can also be used to read them.

Creation of a CHM file is very simple, and it supports extended characters too. However, it does not support Unicode completely.

The feature of compressing the collection of HTML pages is achieved by implementing the LZX algorithm, albeit with a twist. The entire file is divided into intervals of 64 KB while it is compressed, and at any given time, suppose a page in the middle of the file needs to be accessed rather than decompressing the file from the beginning, the CHM format has the ability to begin the decoding process from the nearest 64 KB interval.

The format supports merging two or more .CHM files together.

Limitations of this Format
While optimized to create Help files, because of which a number of applications opt for this format to present their software's Help topics, the CHM format is not equipped to suit documents of most other kinds.

Although CHM files contain HTML pages, this format was designed much before the advent of Cascade Styling Sheets (CSS), which is used abundantly while coding in present versions of HTML. Successfully implementing CSS effects on a CHM Help file is an extremely trying task.

The CHM file format is Microsoft-proprietary. On OS X, or on any other non-Microsoft operating system, files of the CHM format can only be opened in certain web browsers that support them, or with the help of CHM readers.

Methods to Convert CHM Files to the PDF Format
Even nowadays, it is still common among software developers to choose the CHM file format while creating their Help resources. However, from the perspective of the actual user who wishes to access these files, a format with a wider outreach, flexibility, and portability has greater desirability. Since the PDF file format fulfills these conditions, converting CHM files to the PDF format is the most suitable solution for this problem.

CHM files can be converted to the PDF format in the following ways:
1. With the help of Adobe Acrobat 9
Adobe Acrobat 9 inherently possesses the ability to convert files of other formats to the PDF format. Any version of Adobe Acrobat more recent than this one can also be used. This method can only be utilized to retrieve the text, or content of the file. The internal hyperlinks in the CHM file will not be transported to its PDF version.

The conversion can be carried out by following these steps:

Locate the CHM file that you wish to convert into the PDF format on your computer, and open it. Do not use your web browser for this purpose.

In the main menu bar at the top of the screen, select Print.

You will be prompted by the Print Topics dialog box to choose whether you would like to print the entire file or specific headings/pages. Select the option you prefer.

In the window that allows you to modify printing options and other settings, open the General tab.

From the Select Printer menu, choose Adobe PDF.

Click on the button labeled Print.

You will be prompted by the Save As dialog box to save the PDF file.

In this way, if you have Adobe Acrobat 9 installed on your computer, you can effortlessly convert a CHM file into a PDF file.

2. Through Zamzar, the free online service
This very handy tool allows users to convert files that have a size smaller than 100 MB, of almost any format under the sun to another one, for free and without having to download any additional software to your computer to carry out the conversion. It is truly very useful as it supports about 1,000 different file formats, and CHM-to-PDF conversion is also supported.

The process is extremely simple:
Locate the CHM file that you wish to convert to the PDF format on your computer, and upload it to the Zamzar website.

If the file is available online, then alternatively you can enter its URL.

From the drop-down menu that allows you to pick the format to which you wish to convert the file you uploaded/referenced, select PDF.

Provide your email address to which you want the converted file to be delivered.

Subscribing to paid services of Zamzar will enable you to avail of features like the ability to convert files as large as 2GB, a personal inbox, priority, online storage space, and much more. Go to this website and make use of their free conversion service.

3. By using any CHM-to-PDF conversion software
There are a number of good CHM-to-PDF converters available nowadays. Some of these are powerful software that are packed with a number of features. Some applications are even free to download, or can be used for free over the Internet. However, their functionality may turn out to be quite basic, or alternatively, they may be optimized for a specific application; for example, converting .CHM-format ebooks to PDF files.

A number of app options are available to users of Apple products like Mac computers/laptops and iOS-based smartphones or tablets on iTunes and the App Store, because CHM being in the Microsoft format, it cannot be directly viewed in OS X and iOS.

A software called PDFlite is an open-source option that can be used to inter-convert files between PDF and other formats. Apart from performing CHM-to-PDF conversion in a manner similar to how Adobe Acrobat 9's built-in conversion tool does, this software has other handy features such as it can double as a PDF Writer. The software can be downloaded here. Many other similar document converters that do the job also exist.

We hope that through our mini guide, we were able to give you sufficient insight into the characteristics of a CHM format file, as well as help you explore the various options available to you if you wish to convert it into the PDF format.