A Dll file does not work by itself. It is a library file that contains functions or instructions for other programs to use and work. Actual content in a Dll file is not in the code we can understand because all is in machine code.

To read these machine code functions we need to decompile every dll file ,so that machine code can be converted into the High Level languages like C,C++,VB etc. Decompiling (Reverse compiling) is not easy , as we first have to find out that in Which High Level Language any specific .dll file was written.

Reverse engineering for source code of a software is a legal area.  We may also get encoded piece of high level language after all the hard work. Encoding is the way of securing the explicit source code from reverse engineers.

Opening a .Dll file directly with any text editor or any other viewer is not the right option. Some software will reject a file with a warning of  “Unsupported File Type” and some will show you the ugly machine code.

As result of complexities said above , we have many utility tools to deal with .Dll Files.  From Microsoft , DUPS (DLL Universal Problem Solver) tool is used to audit, compare, document, and display DLL information. The following list describes the utilities that make up the DUPS tool:

• Dlister.exe
  This utility enumerates all the DLLs on the computer and logs the information to a text file or to a database file.
• Dcomp.exe
  This utility compares the DLLs that are listed in two text files and produces a third text file that contains the differences.
• Dtxt2DB.exe
  This utility loads the text files that are created by using the Dlister.exe utility and the Dcomp.exe utility into the dllHell database.
• DlgDtxt2DB.exe
  This utility provides a graphical user interface (GUI) version of the Dtxt2DB.exe utility

For more information about DUPS tool , you can visit the link provided below this article.

There are few more third party (Other than Microsoft) utilities tool for .Dll files. All have different use or purpose as a dll file utility tool. Let see some of them -

• DLL Export Viewer v1.45 -  This utility displays the list of all exported functions and their virtual memory addresses for the specified DLL files. You can easily copy the memory address of the desired function, paste it into your debugger, and set a breakpoint for this memory address. When this function is called, the debugger will stop in the beginning of this function

• InjectedDLL v1.00 – InjectedDLL is a small utility that displays the list of DLLs that are automatically injected on every process in your system.

• ResourcesExtract v1.17 – ResourcesExtract is a small utility that scans dll/ocx/exe files and extract all resources (bitmaps, icons, cursors, AVI movies, HTML files, and more…) stored in them into the folder that you specify. You can use ResourcesExtract in user interface mode, or alternatively, you can run ResourcesExtract in command-line mode without displaying any user interface.

• IconsExtract v1.47 – Extract icons and cursors from EXE, DLL, CPL, and OCX files and save them as ICO or CUR files.

• Resource Tuner – Resource Tuner lets you open Windows executable files such as .EXE, .DLL, Device Drivers (.SYS), OCX Controls, and several others. Once inside, you can change the look of the icons, cursors, dialogs, buttons, sounds, animations and other elements of the Windows user interface by editing and replacing resources in the executable files

• ExeInfo v1.01 – The ExeInfo utility shows general information about executable files (*.exe), dynamic-link libraries (*.dll), ocx files, and drivers files.

Most of the tools mentioned above are Free to download and use. But i will like to conclude with a word of caution that do not download such a utility tools from forums or communities sites. Almost every tool is free so download it directly from the creator’s site. I hope you will find this article helpful.