Seafile with nextcloud documentserver

is any oppotunity to use documentserver which go now with nextcloud 18.0

Do you mean the OnlyOffice documentserver? Seafile supports the integration with OnlyOffice documentserver.

no i mean? can i use nextcloud app - documentserver which from 18.0 ver installed as aditional app. Sorry for my bad english(((

You can use Seafile+OnlyOffice Documentserver OR Nextcloud+OnlyOffice Documentserver.
Seafile and Nextcloud are competitors.
You can’t use Seafile+Nextcloud+Documentserver, because Seafile and Nextcloud are the same product category.