Microsoft Word 2007 and later saves documents in the OpenXML format with a .DOCX extension.
You can open it using any of the below application
Microsoft Word 2010
Microsoft Word Viewer
Corel WordPerfect Office X6
Try changing the file association. Right click on the .doc file > click on Open With > Choose program, and select what application you want it to open with. And remember to tick on 'Always use selected program.
Now Wordpad will always have some difficulties reading full fledge .doc files. One way around is to always save or convert your .doc files to .rtf.
You can also open, and use your word files online, and for free on google drive .
And then again, there are plenty of free programs out there that are just like MS word.
Abiword - AbiWord
OpenOffice - Apache OpenOffice - The Free and Open Productivity Suite
Jarte - FREE Word Processor Based on Microsoft's WordPad Engine