I haven't tried this one yet. I tend to write CHM help files from scratch, so have no real need to use it. But it looks like it could be useful for using an existing PDF file as the source of a program's context-sensitive help file.

PDF DocuReader - a simple and comfortable PDF reader for your help and manual files

The free solution for your help system

Use pdf files in your program's help system and as user manuals!

Which tool and which file format do you use for displaying the program help in your software?
Typically, the software of today stores its help in .chm-format. But .chm files are potential carries of security threats and are oft blocked by the security software.
The HTML-format requires a lot of separate files (texts, images etc.).
The HLP-format was introduced with Windows 3.1 and does not correspond to the actual technic level any more. Also, the HLP-Viewer WinHlp32.exe is no more distributed with Windows Vista.
PDF files are a good solution, but a separate reader is required. The free Adobe® Reader provides no possibility to realize a context sensitive help. Besides, Adobe® Reader is no more easily distributable.

The solution: use PDF DocuReader from soft Xpansion! Start the program directly from your application like this:

sx-pdf-docureader.exe PDF_filename optional_page_number

and all the necessary functionality for the help presentation are available.

The PDF DocuReader functions:
Open, read and display any PDF files
Show the needed document page at start
Navigate using the bookmarks, links, buttons "Next page" and "Previous page"
Zoom and search function