Not sure if I understand you 100%, but instead of reading a file through UTL_FILE, nowadays (well, even a decade ago) you can simply query the file, using SQL, if you use an External Table.
Read about them here:
If your data is on a SQL*Server database then you could use either the Database gateway for SQL*Server (DG4MSQL) or the Database Gateway for ODBC (DG4ODBC) to select that data from an Oracle database.
If you have access to My Oracle Support then have a look at these notes for more information -
|Options for Connecting to Foreign Data Stores and Non-Oracle Databases (Doc ID 233876.1)|
Functional Differences Between DG4ODBC and Specific Database Gateways (Doc ID 252364.1)
Gateway and Generic Connectivity Licensing Considerations (Doc ID 232482.1)
and also -
Master Note for Oracle Gateway Products (Doc ID 1083703.1)