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I have a text file text01 created in pf QDDSSCR...
If you have a PF named QDDSSCR, then you cannot "have a text file" in it. A file will not contain another file.
Instead, TEXT01 will be a member of QDDSSCR. (We'd normally assume that the actual name of the file is "QDDSSRC".)
Most PFs can have many members. When you open a file with more than a single member, it's usually necessary to tell your program which member first.
From ILE COBOL Language Reference manual: