Other than Microsoft Office is there any other Software Package available for Windows that is completely free and can also open .docx, .pptx, .xlsx etc... file formats?
The two main options are:
Both are similar and can open the Microsoft Office suite documents with most, but not all unfortunately, functionality and layout preserved.
Other options include:
You should know that the alternatives have lower document fidelity than the real thing but LibreOffice and OpenOffice are capable of opening such files for quite some time now.
Consider using open formats and spreading the word.