Sharing documents has absolutely nothing to do with the operating system, and 100% to do with whether the recipient has a program installed that can read/write the documents you provide. It's not like the 1's and 0's of Windows-based data are any different from the 1's and 0's of Linux-based data.
Someone on Linux who doesn't have a program installed to read Word documents is as disadvantaged as someone with Windows or Mac OS X without a program to read/write them.
It's a good thing, then, that there are at least 3 options available to a Linux user to read documents created with Windows programs:
1) Dual boot. Run Linux normally, but boot into Windows when needed
2) Emulate Windows. Use a virtual machine or compatibility layer like WINE to run the Windows software on a Windows layer from within Linux.
3) Use a Linux program. Find a Linux-compatible program that can use the documents provided. In the case of MS OFfice documents specifically, Open Office can read/write pretty much any file format that MS Office can (not 100% compatible, but close enough for most cases).