Many users, especially those who are used to working with technical documentation or e-books on a PC, encounter an unexpected obstacle when switching to mobile devices. This is the .chm (Compiled HTML Help) format that has been the standard for Microsoft help systems for decades. An attempt to open such a file using the standard means of a modern smartphone often ends in an error or a proposal to download some kind of incomprehensible archiver.
The Android system, by its architecture, does not have a built-in engine for rendering compiled HTML help, so without installing third-party software, access to the contents of such archives is impossible. This is not a defect of the device, but rather a consequence of the evolution of formats: mobile operating systems focus on PDF and EPUB, leaving CHM as a niche standard for specific literature. However, the need for reading such files remains high among engineers, programmers and students.
Fortunately, the Google Play ecosystem offers many solutions that can turn your smartphone into a full-fledged reader for this format. In this article, we will analyze in detail which applications cope with this task best, how to avoid problems with “crazy language” in the text, and what hidden functions may be useful when studying lengthy instructions.
The nature of the CHM format and complexity on mobile platforms
Format CHM is a compressed archive containing a set of HTML pages, images and a table of contents index. It was originally developed by Microsoft to create online help for Windows software products. The main feature is that this is not just text, but a full-fledged web structure, packaged in one file with the extension .chm. It is this structure that creates the main difficulties when porting to mobile platforms.
The compatibility problem arises due to differences in the way hypertext is processed. While desktop browsers and Windows Explorers “understand” internal CHM navigation natively, mobile OSes require emulation of this environment. Simple text editors or even advanced archivers like WinRAR for Android can often only extract files from the container, but not display them as a single document with a working table of contents.
⚠️ Attention: Don't try to simply rename the file extension from .chm to .zip or .rar in the hope of opening it with a standard file manager. Although technically this is an archive, such manipulation will break internal links, and navigation through the document will become impossible without a specialized parser.
In addition, there is an encoding problem. Many old reference books were created in the era of encoding dominance Windows-1251 or even MS-DOS, while modern Android applications use UTF-8by default. Without properly setting up the application, you risk seeing a set of unreadable characters instead of text, which will make reading pointless. High-quality software should automatically detect the encoding or allow you to change it manually.
Review of the best applications for reading CHM on Android
Today, there are several dozen applications in the Google Play store that position themselves as CHM readers. However, not all of them are equally useful. We tested the most popular solutions to highlight those that provide stable operation, user-friendly interface and gesture support. Choosing the right tool depends on your specific tasks: whether you only need to read or also take notes.
One of the market leaders is the application ReadCHM. It features a minimalistic design and high speed of opening even very large files. Users appreciate it for the absence of intrusive advertising in the free version and an intuitive table of contents that syncs with the scrolling text. Another strong player is CHM Reader from the developer Moon+, which offers advanced options for customizing fonts and design themes.
- 📚 ReadCHM is the best choice for quick access and reading on the run, supports bookmarks and navigation history.
- 🛠️ CHM Viewer & Reader is a powerful all-in-one tool with the ability to export pages to PDF and complex encoding settings.
- 🌐 HtmlCHM is a universal solution that can also open regular HTML files and has a built-in search for content.
New generation archiver applications, such as ZArchiverdeserve special mention. Although their main function is working with archives, recent updates have added support for CHM previews. This is convenient if you don’t want to install a separate application just for a rare occasion, but the reading functionality here will be reduced compared to specialized readers.
Step-by-step guide: installing and setting up the reader
The installation and initial setup process does not require deep technical knowledge, but has its own nuances that will ensure comfortable reading in the future. Follow this algorithm to avoid common beginner mistakes. First, you need to download the selected application from the official store to ensure that there is no malicious code.
After installation, launch the application. On the first screen, you will likely be asked to grant permission to access your device storage. This is a required step, since without rights to read the internal memory or SD card, the app simply will not see your files. In modern versions of Android (starting from 11 and higher), access may be requested to specific folders, and not to the entire storage at once.
☑️ Preparing to read CHM
Next, find your file through the app's built-in file manager or use system explorer. When you first open a document, pay attention to how the text appears. If you see hieroglyphs instead of letters, go to the application settings (usually a gear icon or three dots in the corner) and look for the item Encoding or Encoding. Try switching the value to Windows-1251, KOI8-R or UTF-8 until the text becomes readable.
For ease of navigation, it is recommended to enable the display of the table of contents panel. In most applications, it is called up by swiping from the left edge of the screen or by clicking on the list icon. This allows you to instantly navigate between chapters, which is critical when working with technical documentation where you need to quickly find specific parameters or commands.
Solving encoding and display problems
The "cracking" problem is the most common user complaint when working with the CHM format on Android. This is due to the fact that encoding metadata inside the file may be missing or incorrect. If automatic detection does not work, you will have to act manually. Advanced readers, such as CHM Viewer, have a function to force an encoding change on the fly without reloading the file.
In some cases, the problem lies not in the application, but in the file itself. If the document was created a long time ago or has compilation errors, it may contain mixed encodings. In such a situation, converting the file on your computer before transferring it to your phone helps. Using utilities like chm2pdf on a PC allows you to convert a problematic file into a universal PDF that opens on any device without unnecessary settings.
⚠️ Attention: If, after changing the encoding, the text becomes readable, but the pictures or formatting are missing, try clearing the application cache in the Android settings (
Settings → Applications → [Your application] → Memory → Clear cache). This will reset the temporary rendering files.
It is also worth considering the font size. Technical documentation often contains tables and code that, when the font is greatly enlarged, can “crawl” off the screen. In the display settings, find the option Fit to width (Fit to screen width) or disable text scaling, leaving only scaling the entire page. This will preserve the integrity of tables and schemas.
What if the file does not open at all?
If the application throws an error when you try to open the file, it may be damaged. Try opening the same file on your computer. If it works there, the problem is the compatibility of the CHM version and the application. Try another app from our list. If the file does not open anywhere, it is damaged when downloading or copying.
Comparative table of the functionality of popular applications
To make it easier for you to choose the right tool, we have compiled a summary table of the main characteristics of market leaders. Pay attention to the presence of advertising and support for additional features such as night mode or voiceover, as these little things significantly affect the user experience in the long run.
| App | Free version | Advertising | Bookmark support | Change encoding |
|---|---|---|---|---|
| ReadCHM | Yes | Minimum | Yes | Automatic |
| CHM Viewer | Yes | Yes | Yes | Manual |
| HtmlCHM | Yes | Absent | No | Automatic |
| ZArchiver | Yes | Yes | No | Limited |
As can be seen from the table, ReadCHM offers the most balanced set of functions for the average user. If manually setting up encodings for old books is critical for you, then CHM Viewer will be a better choice, despite the presence of advertising, which can be disabled in the paid version.
Additional features and optimization tips
Modern readers offer functions that go beyond simply displaying pages. For example, many of them support searching text within a file. This is an indispensable tool when searching for a specific command in a programming reference. To activate the search, you usually just need to click on the magnifying glass icon and enter a query - the application will highlight all occurrences.
Another useful feature is the night mode. Reading technical literature often takes place in low light conditions, and a white background can tire the eyes. Turn on inverted colors or sepia in the theme settings to reduce eye strain. Some applications, such as Moon+ Reader Pro (with plugin support), even allow you to adjust the screen color temperature programmatically.
If you are reading CHM with diagrams and diagrams, turn on Landscape mode (horizontal orientation). This will significantly increase the usable screen area for displaying complex graphic elements without the need for constant zooming.
Don't forget about synchronization. If you start reading a book on your phone in public transport and continue on your tablet at home, look for apps that support cloud synchronization of your reading progress. Although this is rarely implemented for the CHM format, some advanced readers allow you to export a list of bookmarks to a text file that can be transferred to another device.
Specialized applications for CHM provide not only reading, but also correct operation of navigation through the table of contents, which is impossible when simply opening the file as an archive.
Frequently asked questions (FAQ)
Is it possible to open a CHM file without installing applications?
Unfortunately, no. The standard Android file system does not have a built-in parser for this format. The only option without installing software is to use online converters in the browser by uploading the file to the site and downloading it in PDF format, but this requires the Internet and is unsafe for confidential documents.
Why do empty folders appear in the table of contents?
This is a common problem with old files where the directory structure was set incorrectly. Try switching the table of contents display mode in the application settings from “Tree” to “List” or vice versa. Updating the application to the latest version also helps.
Is it safe to open CHM files from unknown sources?
The CHM format can theoretically contain malicious scripts, although on Android the risk of their execution is minimal due to the sandbox. However, download technical documentation only from official websites of manufacturers or verified repositories.
How to convert CHM to PDF on a phone?
Direct conversion on a phone is difficult. It's best to use the "Print" function in the reader application (if it has one) and select the "Save as PDF" virtual printer. Or use online conversion services through a mobile browser.
Do these applications support files in Russian?
Yes, all applications listed in the article support Cyrillic. The main condition is the correct choice of encoding in the settings, if it is not detected automatically. Modern versions of applications usually work correctly with UTF-8 and Windows-1251.