What Software Opens DLL Files for Free: A Comprehensive Guide

DLL files, short for Dynamic Link Library, are fundamental components in the Windows operating system. They contain code and data that multiple programs can use simultaneously, promoting code reusability and efficient memory management. While DLLs are essential, they’re not meant to be directly opened and viewed like regular documents or images. However, there are situations where you might need to examine a DLL’s contents, whether for debugging, understanding software dependencies, or simply for educational purposes. This article will guide you through various free software options that allow you to peek inside DLL files, providing step-by-step instructions for each method.

Understanding DLL Files: Why Can’t You Just Open Them?

Before we dive into the ‘how,’ it’s crucial to understand the ‘why.’ DLL files are not executable programs themselves; they are libraries of code that programs use. They typically contain compiled functions, resources (like icons or strings), and other data necessary for application functionality. Therefore, double-clicking a DLL file won’t launch a program; instead, Windows will likely prompt you to choose an application to open it, which often leads to an error because it’s not designed to be opened in that way.

Think of a DLL file as a toolbox. A carpenter (an application) uses the tools (functions and data) inside the toolbox but doesn’t directly try to ‘open’ the toolbox as if it were a completed project. You wouldn’t try to ‘open’ a screwdriver like a door, would you? Similarly, you shouldn’t try to open a DLL like a document.

When Would You Need to ‘Open’ a DLL File?

Despite their indirect nature, there are valid reasons to want to examine the contents of a DLL file:

• Debugging: If an application is crashing or behaving unexpectedly, examining the DLLs it uses can help pinpoint the source of the issue.
• Dependency Analysis: To understand what other DLLs a particular program relies on, which is important for troubleshooting software conflicts or for packaging software correctly.
• Security Analysis: In some cases, security professionals may want to examine DLL files for potential malware or vulnerabilities.
• Reverse Engineering: While ethically complex, examining DLL files is part of the reverse engineering process, often done for research or interoperability purposes.
• Learning: Simply to learn more about how programs work under the hood.

Free Software Options for Examining DLL Files

Now, let’s get to the practical part. Here are some of the most popular and free tools you can use to explore the contents of DLL files:

1. Dependency Walker

Dependency Walker is a classic utility that specializes in identifying the dependencies of Windows executables and DLLs. It provides a hierarchical view of all the DLLs a program uses, making it excellent for dependency analysis. While it doesn’t allow you to directly see the source code (which is often not present in compiled DLLs), it provides vital information about what modules are used, what functions they export, and any missing DLL dependencies.

Steps to Use Dependency Walker:

1. Download and Install: Download Dependency Walker from a trusted source (e.g., the official website) and install it.
2. Run Dependency Walker: Open the Dependency Walker application.
3. Open the DLL File: Go to “File” > “Open” and navigate to the DLL file you want to examine. Select the DLL and click “Open.”
4. Explore the Tree View: Dependency Walker will now analyze the DLL and show a tree view in the left pane, displaying the DLL’s dependencies. The right panes show detailed information, such as exported functions, import functions, and other module properties. You can expand nodes in the tree to delve deeper into the dependency chain.
5. Understand the Information: Look at the list of imported DLLs on the left pane and explore exported function names and ordinal values of selected DLL on the right hand side panes. Note down any missing dependencies (indicated with error icons) if there are any.

Benefits of Dependency Walker:

• Excellent for dependency analysis.
• Free to use.
• Lightweight and efficient.

Limitations of Dependency Walker:

• Doesn’t display source code.
• Primarily focused on dependencies, not comprehensive file viewing.

2. Resource Hacker

Resource Hacker is another free utility that excels at viewing and even modifying resources embedded within executable files (EXEs) and DLLs. Resources can include dialog boxes, menus, icons, strings, bitmaps, and more. This tool is ideal if you’re interested in the visual and textual elements stored inside a DLL.

Steps to Use Resource Hacker:

1. Download and Install: Download Resource Hacker from a reputable source (e.g., the official website) and install it.
2. Run Resource Hacker: Launch the Resource Hacker application.
3. Open the DLL File: Go to “File” > “Open” and navigate to the DLL you want to examine. Click “Open.”
4. Explore the Resource Tree: The left pane will display a tree view of the various resources contained in the DLL. Expand the nodes (e.g., “Bitmap”, “Icon”, “String Table”, “Dialog”) to browse each type of resource.
5. View Resource Contents: Select an item in the tree, and the corresponding resource content will be displayed in the right-hand pane (e.g., a preview of an image, the content of a string).
6. Note: Be cautious when making changes. Resource Hacker allows modification of resource, but making mistake while modifying files can render your system unstable.

Benefits of Resource Hacker:

• Excellent for viewing and editing embedded resources.
• Free to use.
• User-friendly interface.

Limitations of Resource Hacker:

• Doesn’t show source code.
• Not primarily meant for dependency analysis.
• Modifying DLL content can damage your system if done incorrectly.

3. PE Explorer

PE Explorer is a sophisticated tool for analyzing Portable Executable files, including DLLs. While it offers more than just a ‘view’ function, its free evaluation version still provides valuable insights into a DLL’s internal structure. It allows you to examine headers, sections, imports, exports, resources, and other low-level information.

Steps to Use PE Explorer (Evaluation Version):

1. Download and Install: Download PE Explorer from the official website and install it.
2. Run PE Explorer: Launch PE Explorer.
3. Open the DLL File: Go to “File” > “Open File” and browse for your DLL. Click “Open.”
4. Explore the Tabs: The main window is divided into several tabs: “File Header”, “Section Headers”, “Import Table”, “Export Table”, “Resources”, and more. Click through the tabs to view the different types of data related to the DLL.
5. Analyze the Data: The data displayed under each tab can be technical, but useful for advanced analysis. For example, the Import Table will show the DLLs this DLL depends on, and Export Table displays the functions it makes available to other modules.
6. Note: the free version comes with some limitations.

Benefits of PE Explorer:

• Advanced analysis features even in the free evaluation version.
• Comprehensive display of file structure.
• Offers insight into headers, sections, imports, exports, resources, etc.

Limitations of PE Explorer:

• The evaluation version has some limitations (certain options might be disabled).
• Can be overwhelming for beginners due to the technical nature of its displays.
• Not truly free, has pay to use version.

4. Notepad (or other Text Editors) – For Simple String Extraction

While not designed for DLL analysis, a simple text editor like Notepad can still reveal some basic information. DLL files often contain readable strings (textual data). You can open the DLL in a text editor and search for these strings to glean some basic information, like author names, error messages, or copyright notices.

Steps to Use Notepad:

1. Run Notepad: Open the Notepad application (or your preferred text editor).
2. Open the DLL File: Go to “File” > “Open.” In the “Open” dialog, select “All Files” from the drop-down menu to see all files, otherwise, by default it shows only .txt files. Navigate to your DLL file and click “Open.”
3. Scroll and Search: The DLL will appear as gibberish or binary data. However, intermixed within this you will find readable strings. Use the “Edit” > “Find” option (or Ctrl+F) to search for specific terms or phrases.

Benefits of Notepad for DLLs:

• Very easy to use, commonly available.
• No installation needed.
• Can reveal readable strings quickly.

Limitations of Notepad for DLLs:

• Not designed for DLL analysis.
• Shows a lot of binary garbage data which may not be readable.
• Limited in functionality.
• Cannot show any structure.

5. Other Hex Editors

Hex editors are tools that display the raw binary data of a file, represented in hexadecimal (base-16) format. These editors are useful if you need to look at very low-level data in a DLL, although they don’t typically provide any contextual information. Some examples of free hex editors include HxD, and Free Hex Editor Neo.

Steps to Use Hex Editors

1. Download and install: Download a hex editor of your choice from their respective website. (e.g. hxd from https://mh-nexus.de/en/hxd/ and Free Hex Editor Neo from https://www.hhdsoftware.com/free-hex-editor)
2. Open the DLL file: Open the hex editor and then open the dll file you want to analyze using the File > Open menu.
3. Analyze the hex data: These editors will display raw bytes of the file in hex format. Analyze the data based on your requirement.

Benefits of Hex Editors:

• Shows the raw binary data of the file.
• Great for advanced analysis.
• Can be used to modify DLLs at a byte level.

Limitations of Hex Editors:

• Requires good knowledge of data representation.
• Not recommended for beginners.
• Modifying binary data can damage your system if done incorrectly.

Important Considerations and Cautions

• Administrator Rights: For some tools (especially for modifying resources), you might need administrator rights to run the application or open the DLL.
• Backup First: If you are tempted to modify a DLL, always make a backup of the original file. If you make an error, you can restore the original file.
• DLLs Are Not Meant to Be Modified: Modifying DLLs can easily break software. Unless you have a very specific reason (e.g. if you are debugging a software with specific instruction), it’s usually best to only view the contents of a DLL. Avoid changing or replacing DLL files you find on your system.
• Security: Be extremely careful when opening DLL files you’ve downloaded from untrusted sources. They can contain malware. Always ensure that the files and software you download are from reputable websites or sources.
• Legality and ethics: Be mindful of the legality of your activity. Some activities like reverse engineering and modifying DLLs might be prohibited or governed by license agreements.

Conclusion

While DLL files aren’t designed for direct viewing, the tools we’ve discussed provide a way to examine their content for various purposes, including debugging, dependency analysis, resource extraction, and learning. Each tool has its strengths and weaknesses, so choose the one that best suits your particular task. Always exercise caution when handling DLL files, especially when modifying them, as incorrect modifications can lead to system instability. Remember, the purpose of examining DLLs is often for analysis and understanding, rather than direct modification. Use these tools responsibly and for legitimate purposes.