A family of Microsoft word processing software products for creating web, email, and print documents.
2 ways, apply the theme to a document 2010, then save it to your 2013 installation or copy the .THMX file
Send the Document
Themes travel with the document
Have the recipient save the custom Theme, with current name, to their local HD: Design tab > Themes group > Save Current Theme. Or in Word Page Layout tab > Themes group > Themes drop down > Save current Theme (use the default theme name)
Distribute the THMX file
Copy the THMX file to the standard Theme location: C:\Users*username*\AppData\Roaming\Microsoft\Templates\Document Themes. The exact location varies slightly depending on the OS.