G Suite documents and corresponding export MIME types

G Suite formats and supported export MIME types map to each other as follows:

Google Doc Format Conversion Format Corresponding MIME type
Documents HTML text/html
HTML (zipped) application/zip
Plain text text/plain
Rich text application/rtf
Open Office doc} application/vnd.oasis.opendocument.text
PDF application/pdf
MS Word document application/vnd.openxmlformats-officedocument.wordprocessingml.document
EPUB application/epub+zip
Spreadsheets MS Excel application/vnd.openxmlformats-officedocument.spreadsheetml.sheet
Open Office sheet application/x-vnd.oasis.opendocument.spreadsheet
PDF application/pdf
CSV (first sheet only) text/csv
(sheet only) text/tab-separated-values
HTML (zipped) application/zip
Drawings JPEG image/jpeg
PNG image/png
SVG image/svg+xml
PDF application/pdf
Presentations MS PowerPoint application/vnd.openxmlformats-officedocument.presentationml.presentation
Open Office presentation application/vnd.oasis.opendocument.presentation
PDF application/pdf
Plain text text/plain
Apps Scripts JSON application/vnd.google-apps.script+json

Call about.get to get an About resource. The About resource contains an exportFormats field with a list of all supported export formats supported by the system for this user.