I am using a 30 day trial of Adobe Acrobat XI Pro, when I convert a pdf to word doc, it has several hidden letters & symbols, is this because it is a trial?
Your PDF probably contains these hiddens characters as well. There is an easy way to check under the Tools pane > Protection panel > Remove Hidden Information command. You can run the command and see what is hidden before actually deleting the hidden content.
Also be aware that the conversion to WORD is a hit-and-miss affair. A lot depends on the structure of the PDF and how it was created. Some files convert almost perfectly for basic text and graphics (equations would generally convert as images), while others have little in common with the view of the PDF.