If you have a fairly simple text document without a lot of graphics, you may be able to have your customers edit the document in WordPad. WordPad is a basic word processor that is included with almost all versions of Microsoft Windows from Windows 95 onwards.
In order for WordPad to open a Word document, the Word document must have a .docx file extension. The formatting may change somewhat but it will allow for editing and the ability for your customers to send the plan back to you electronically. Not a perfect solution but it may work.
Kind Regards, Jacquie