Every time I download a pdf file it becomes converted into another type of file format. When you try to open the document it says:
Select the encoding that makes your document readable.
Windows (default) MS-DOS Other encoding
How can I stop this from happening and just open in a pdf file format?
Are you talking about the help files in PDF format (this forum is about Adobe's "help files" application, not help about Adobe applications)?
If not, you should post in the adobe reader forum: http://forums.adobe.com/community/adobe_reader_forums
This sounds to me like a file association problem. If so, the solution (OS dependant) is more or less on these lines:
Select a file you know is a PDF. Right click to see its properties. In Open with, choose Reader, and click on Apply to all.