Regarding how can i use backspace in DocIO: We suspect that your requirement is to remove some elements in the Word document. Essential DocIO is a non-UI component that provides a full-fledged document instance model similar to the Microsoft Office COM libraries to iterate with the document elements explicitly and perform necessary manipulation. To achieve your requirement we suggest you to iterate through the document elements and remove the element using DocIO.
If you face some difficulties to find and remove the particular the element in the Word document, you can also use find and replace functionality and replace with empty value.
Regarding can i convert this part of code from word9 to DocIO: From the given code example, we suspect that your requirement to remove the bookmark contents and table in the Word document. You can iterate into the Word document and remove the elements using DocIO.