Batch Word Replace - Replace text in, add or remove content, and edit thousands of Word documents in doc and docx formats, PDFs, RTF documents, and other text documents.
Okular - Okular is a universal document viewer based developed by KDE.
Search and Replace - Don't worry about those many files where you have to change a few things!
Sumatra PDF - Sumatra PDF is a slim PDF/DjVu/EPUB/XPS/CHM/CBR/CBZ/MOBI viewer for Windows.
Actual Search And Replace - This is an advanced tool to perform the search and replace operations across multiple text files. It supports the regular expressions syntax. The batch replace operation allows to execute a lot of various replacements with one click.
Foxit Reader - Foxit Reader is a free and light-weight multi-platform PDF document viewer.