稍後翻譯，來自 https://community.oracle.com/thread/1101968

*1) i got a .dmp file obtained by an export. (not sure whether its exp or expdb)*

If in windows environments we can find the export type by using the following:
type dumpfile.dmp | more
for eg: Normal export method:
D:\050710>type fullbkp.dmp | more
♥
▓EXPORT:V09.02.00
DHELPDBA
RENTIRE
2048
0
20

0

Now from the above you can identify it has normal export method.

For Datapump export Method:
F:\Oracle_Backup>type DBBKPFULL.DMP | more
☺☺~N⌠╩
gÇ╝
☺;Ö☺§(±l#ºN»ê&
íHYóo
☺
►
▓┌☺ ♦♦
☻☻
☺▼*
╖Äx
"HOVDBA"."SYS_EXPORT_FULL_01"

Now from the above you can identify it has datapump export method.

*2) is there a way to me to import this dumpfile to a fresh database without knowing the source schemas ??*

In normal export method you can use show=y

imp system/password file=dumpfile.dmp log=logfile.log full=y show=y

In datapump export method you use sqlfile option:

impdp system/password directory=direct_name dumpfile=dumpfile.dmp logfile=logfile.log sqlfile=toknowschema.log full=y exclude=table_statistics,index_statistics

If you use full=y alone it wil import the entire database objects from the dumpfile.

If you use full=y & show=y options together, it means entire database objects scripts will be spooled into log file mentioned.

In your case check the logfile used by you ie : exp-full-20100715.log 

You can find the exported schema details in that