How to Read a DLL File: View Its Code and Contents

What You’ll Need

A Windows computer, or a compatible analysis environment, and the DLL file you want to inspect. If you did not obtain it from a source you trust, do not run or register it.
A tool suited to what you want to see. A .NET decompiler can show managed code; a PE viewer can show file structure and metadata; a resource viewer can display icons, dialogs, and other embedded assets. Choose software from its official publisher or a reputable project page.
Basic caution with unknown files. Work on a copy, keep security software enabled, and avoid uploading private or proprietary files to online analysis services.

Step-by-Step

Decide what “read” means. A DLL (dynamic-link library) contains code or data that Windows programs can use. You might want to identify its publisher and architecture, browse embedded images or text, or inspect code. These are different tasks, so select a tool accordingly. A DLL is not necessarily source code, and opening it will not always reveal readable text.
Check the file before opening it. Confirm the file name and extension, and consider where it came from. A name ending in .dll does not prove the file is safe or genuine; malware can use that extension too. If the file arrived unexpectedly, came from an unknown download, or is supposed to be part of Windows, do not launch it to “see what happens.” Obtain system files through trusted Windows tools or official software sources instead.
Make a working copy. Copy the DLL to a separate folder and leave the original unchanged. If you only need to inspect it, you generally do not need to install, register, or execute it. Avoid changing permissions or moving a DLL out of an application’s installation folder just to make the application work; that can break software.
Choose a viewer that matches the DLL. For a .NET assembly, use a reputable .NET decompiler that supports browsing assemblies and their metadata. For a general Windows executable-format inspection, use a PE (Portable Executable) viewer. For icons, menus, or dialog resources, use a resource viewer. Check the tool’s official documentation and download source. Do not disable antivirus protection just because a tool or file triggers a warning.
Open the copy inside the tool. Start the viewer first, then use its Open or Browse command to select your copied DLL. Menu labels and locations may differ slightly by version. If Windows asks whether to run or install the file, cancel; a viewer should inspect it rather than execute it.
Inspect the basic information. Look for the file format, target architecture (such as 32-bit or 64-bit), version details, and any available publisher or signature information. A digital signature can help identify a publisher and whether a file has changed since signing, but it does not by itself guarantee that a file is harmless.
Browse the content you need. In a decompiler, expand the assembly’s namespaces, types, and methods to view reconstructed code. In a resource viewer, select the resource categories to preview images, strings, or dialogs. In a PE viewer, examine sections, imports, and exports. These views describe different parts of the file; imports and exports are function references, not necessarily complete source code.
Interpret results carefully. Decompiled output is a reconstruction, not the original source. Names may be shortened or removed, comments are generally absent, and compiler optimizations can make the logic difficult to follow. Native-code DLLs may show assembly instructions or structural details rather than clean, high-level code. Do not assume that a string or function name alone proves what the DLL does.
Close without changing the file. Unless you have a specific, authorized reason and understand the consequences, do not edit, replace, or save over the DLL. Close the viewer and retain or delete your working copy according to your needs. If you found the DLL because an app reports an error, use the app’s official repair or reinstall process rather than downloading a replacement DLL from an unfamiliar site.

Common Mistakes

Opening it in Notepad: DLLs are binary files. A text editor may show scattered readable strings mixed with unreadable characters; that is not the complete code and can be confusing.
Expecting one tool to show everything: A resource viewer may not decompile code, and a .NET decompiler may not explain native machine code. Identify the file type and goal first.
Running or registering the DLL: A DLL is normally loaded by another program. Running or registering an unknown file can cause security or system problems and is unnecessary for basic inspection.
Replacing a missing DLL from a random website: A similarly named file may be incompatible, altered, or unsafe. Repair the program or Windows component using its official source.
Treating decompiled output as exact source: Decompilation can omit information and produce approximate code. Use it as an aid to understanding, not as proof of the original author’s intent.

Tips

Keep a note of the file’s original location, exact name, and any version details before investigating it.
Use a separate analysis environment, such as a properly isolated virtual machine, if you have a legitimate need to examine a suspicious file. Isolation reduces exposure but does not make unsafe handling risk-free.
For a DLL that belongs to an installed program, check that program’s documentation or support resources. They may explain its purpose without requiring code inspection.
When comparing two DLLs, compare their digital signatures, version information, and cryptographic hashes with trusted reference values where available. A matching filename alone is not a reliable comparison.
Menu paths and features in analysis tools can differ by version. Use the tool’s current help pages rather than following instructions for an unfamiliar or outdated interface.

Troubleshooting

The tool says the file is not a valid assembly: It may be a native-code DLL, a different file type, damaged, or mislabeled. Try a PE viewer for structural details; do not keep renaming extensions or opening it in random applications.

The decompiler shows unreadable output: The DLL may use native machine code, be obfuscated, or contain optimized code. A .NET decompiler will not turn every DLL into readable C#; use a compatible viewer and consult its documentation.

The file cannot be opened or access is denied: Confirm the path and that you selected the copy. Another program may be using the file, or your account may not have permission. Do not change system-file permissions or stop security software to force access.

You see a security warning: Stop and verify the file’s source and the analysis tool’s publisher. Do not whitelist the file or disable protection merely to continue. If it is unexpected, delete it or ask your organization’s IT or security staff to review it.

An app says the DLL is missing: Do not download an individual DLL from an unverified site. Use the application’s official repair or reinstall option, or consult its support documentation. For a Windows component, use Windows’ built-in repair guidance or Microsoft Support.

Frequently Asked Questions

Can I read a DLL as plain text?

Not reliably. A text editor may reveal some embedded strings, but most DLL content is stored in binary form. Use a format-aware viewer for useful information.

Can I see the original source code?

Usually not. A decompiler can reconstruct an approximation from compiled code, especially for some managed .NET files, but it cannot reliably restore original comments, formatting, or all names.

How can I tell whether a DLL is 32-bit or 64-bit?

Open it in a PE viewer or file-inspection tool and check its architecture or machine-type field. Do not infer architecture from the filename alone.

Is it safe to open a DLL?

Inspection with a reputable viewer is different from executing the file, but unknown files still deserve caution. Use a copy, keep security protections on, and avoid running or registering it.

Can I edit a DLL to fix an error?

Editing compiled files is risky and can make the application fail or introduce security problems. Use the software publisher’s repair, update, or reinstall instructions instead.

Why does a DLL show strange characters in a text editor?

Because it is a binary executable-format file, not a text document. The editor is interpreting bytes as characters, so the display is not a meaningful representation of the whole file.

Further reading: Microsoft Support. Details can change, so check the official page for anything that matters to you. Spotted a mistake? Tell us. How we write an answer.