ORA-00997: illegal use of LONG datatype

While copying the data from one database to another using database
link. For the tables which has long data types, its giving the error :

1)insert into DOC select * from DOC@acc_link
ORA-00997: illegal use of LONG datatype

Unfortunately, you cannot do an "insert into select" for tables with long datatype columns. If what you're trying it outside of PLSQL or any applications then you can use the COPY command available with SQLPLUS to copy over the data. The syntax is this:
Login to the destination table schema through SQLPLUS and once logged
in, try this:

SQL> copy from /@
insert DOC using select * from DOC

For the above statement to work, you don't need a database link. The statement is login in to the source database using the username and password you supply.