If you supply the preformatted articles (text content) to APM, they are generally kept. However, the outcome depends on the APM formatting settings.

Article elements formats

The article elements formats are always ignored and the shape formats applied instead.

This requires that the general preference (Edit > Preferences > Extra > General > When Linking) Keep Local Formats is ticked.

Article elements styles

The article elements styles and tags are kept unchanged if the Auto-Apply Styles preference is unticked. Otherwise, the original styles and tags are removed, before applying the styles, specified in frames parameter. See APM and plain text.

Note about original styles and shape formats

In order for the original styles to work even when the formats get applied from the library shapes, the styles MUST BE AVAILABLE in every format, applied on the library shapes.

An example: in your headlines, you use the style "RedH" that stands for the "red highlight". The headlines can be paginated in headline boxes of, let's say, 73 shapes in various object libraries. Those 73 shapes use 48 different headline formats. To all those 48 headline formats you must link a library of styles that contains the definition the RedH style. Otherwise, the text formatting error will occur and the headline will not be properly formatted.

See also

APM and plain text