When you save email conversations to Google Drive, you can select from the following options for the export format:

1. Export to PDF format
2. Export to HTML format (web pages)
3. Export to TXT format (plain text)
4. Export to EML format (email archive – attachments are embedded in EML). It can be used to import..

Export to PDF format

When you select this option, each file will be saved using PDF (Portable Document Format).

For example, if you select three email conversations:

…each conversation is saved as a separate PDF file.

Export to HTML format (web pages)

When you select this option, each file will be saved using the Hypertext Markup Language (HTML) format.

For example, if you select three email conversations:

…each email conversation is saved as a separate HTML file:

Export to TXT format (plain text)

When you select this option, each file will be saved using the plain text (TXT) format,

For example, if you select three email conversations:

…each email conversation is saved as a separate TXT file:

Export to EML format (email archive – attachments are embedded in EML)

When you select this option, each file will be saved using the Electronic Mail (EML) format.
This format allows you to restore files back into Gmail. For instruction how to that click check this support note: How to restore emails from cloud app’s email backup

For example, if you select three email conversations:

…each email conversation is saved as a separate EML file: