I've updated my answer, because it was an answer for a case when table columns are involved, but the word column in the question mean a column or text rather than a column in a table.
In the document, You should be able to get the following values:
// ...
var sectionProperties = body.GetFirstChild<SectionProperties>();
// pageSize contains Width and Height properties
var pageSize = sectionProperties.GetFirstChild<PageSize>();
// this contains information about surrounding margins
var pageMargin = sectionProperties.GetFirstChild<PageMargin>();
// this contains information about spacing between neighbouring columns of text
// this can be useful if You use page layout with multiple text columns
var columns = sectionProperties.GetFirstChild<Columns>();
var spaceBetweenColumns = columns.Space.Value;
var columnsCount = columns.ColumnCount.Value;
I haven't tested this, but I suppose You may be able to calculate the actual width of a text column using those values.