Some of the are supported document formats (with varying degree of accuracy) are listed below. Please try this app with few files before importing in bulk.
Markdown (CommonMark Markdown, GFM etc.)
Microsoft Word (Word docx) (except embedded images)
You can also try to import following file formats as this add-on is based on Pandoc file convertor which can convert them. However, please note that these formats are not tested properly.
Dokuwiki (DokuWiki markup)
Creole (Creole 1.0)
FictionBook2 (FictionBook2 e-book)
Haddock (Haddock markup)
Jupyter/IPython notebook (Jupyter notebook)
JATS (JATS XML)
JSON (JSON version of native AST)
Mediawiki (MediaWiki markup)
EMACS Org mode (Emacs Org mode)
Tikiwiki (TikiWiki markup)