Unfortunately, Amazon RDS for Oracle does not provide a direct equivalent to the traditional CREATE PFILE FROM SPFILE command that you would use in on-premises Oracle databases. In standard Oracle environments, all instance and database-level parameters are stored in a binary Server Parameter file (SPFILE), which can be exported to a text file using the command CREATE PFILE = 'my_init.ora' FROM SPFILE = 's_params.ora' [1].

Available RDS Alternative for SPFILE Management

Amazon RDS does provide a procedure specifically for validating the SPFILE. You can use the rdsadmin.rdsadmin_rman_util.validate_spfile procedure to validate the server parameter file used by your RDS Oracle DB instance [2]. However, this validation procedure does not export or display the SPFILE contents in a readable text format.

Recommended Approach for Parameter Management

Instead of exporting the SPFILE, you should manage and review your Oracle database parameters through Amazon RDS parameter groups, which are accessible via the AWS Management Console, AWS CLI, or RDS APIs. This managed approach provides visibility into your database configuration without requiring direct file system access to the SPFILE itself.

As mentioned in AWSCLI document(https://docs.aws.amazon.com/cli/latest/reference/rds/describe-db-parameters.html) you can describe and get the details of parameters in parameter group using below command.

aws rds describe-db-parameters --db-parameter-group-name <parameter-group-name> 

You can export them to textfile by using below command.

aws rds describe-db-parameters --db-parameter-group-name <parameter-group-name>  > paramfile.txt

References:

[1] Title: "Oracle instance parameters and Amazon RDS parameter groups - Oracle to Aurora PostgreSQL Migration Playbook" URL: https://docs.aws.amazon.com/dms/latest/oracle-to-aurora-postgresql-migration-playbook/chap-oracle-aurora-pg.configuration.parameters.html

[2] Title: "Validating database files in RDS for Oracle - Amazon Relational Database Service" URL: https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/Appendix.Oracle.CommonDBATasks.ValidateDBFiles.html

In Oracle databases, including those running on Amazon RDS for Oracle, you can export the Server Parameter File (SPFILE) to a text Parameter File (PFILE) using the standard Oracle command:

CREATE PFILE = 'my_init.ora' FROM SPFILE = 's_params.ora';

This command works the same way in Amazon RDS for Oracle as it does in on-premises Oracle databases. The binary SPFILE contains all Oracle instance and database-level parameters that were configured using the ALTER SYSTEM command.

When working with Amazon RDS Custom for Oracle, you have more flexibility with parameter files. For example, when migrating to RDS Custom, you don't necessarily copy the SPFILE from the source database. Instead, you can use the standard parameter file (PFILE) created with the Amazon RDS Custom DB instance and add the parameters you need. The RDS automation creates a backup of the init.ora file (called oracle_pfile) in the /rdsdbdata/config directory.

Remember that when working with parameter files in Amazon RDS Custom, you should not alter certain values provided by the Amazon RDS Custom PFILE, such as control_files and db_unique_name, as Amazon RDS expects these specific values.
Sources
Oracle instance parameters and Amazon RDS parameter groups - Oracle to Aurora PostgreSQL Migration Playbook
Oracle instance parameters and Aurora MySQL parameter groups - Oracle to Aurora MySQL Migration Playbook
Migrate Oracle E-Business Suite to Amazon RDS Custom - AWS Prescriptive Guidance

This is a very common question for DBAs moving from on-premises environments to AWS. You are correct that you cannot run the standard CREATE PFILE FROM SPFILE comm and on an RDS for Oracle instance. The reason is that RDS is a managed service, which means you do not have direct access to the underlying server's file system, so there is no path where RDS could write the text file for you.

However, you can easily achieve the same result using the AWS-native method for parameter management: Parameter Groups. All of your database initialization parameters are stored within the parameter group associated with your RDS instance. To get a text file equivalent of a pfile, the most effective method is to use the AWS Command Line Interface (CLI). You can run a command to describe all the parameters for your specific parameter group and redirect the output to a file. This gives you a complete, exportable record of all settings. The command would look like this:

aws rds describe-db-parameters --db-parameter-group-name <your-parameter-group-name> > my-rds-pfile.txt

This command will query the RDS service for all parameters in the specified group and save the output (which is typically in JSON format) to a text file named my-rds-pfile.txt. This file serves the exact same purpose as an on-prem pfile: it provides a complete, versionable, and readable record of your database's configuration. For quick checks of individual parameters, you can also view them directly in the AWS Management Console under the "Parameter Groups" section for your RDS instance, or you can query the V$PARAMETER dynamic view from a SQL client connected to the database.