How to access both DocumentDB and S3 in the same Java program

Hello,

I have a Java Spring Boot 2 application that needs to connect to both DocumentDB and S3.

As stated on https://docs.aws.amazon.com/documentdb/latest/developerguide/connect_programmatically.html I downloaded rds-combined-ca-bundle.pem, created a truststore and specified the system parameter javax.net.ssl.trustStore. As a result I can connect to DocumentDB with TLS but when I connect to S3 using the java SDK I now get

com.amazonaws.SdkClientException: Unable to execute HTTP request: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
in
com.amazonaws.services.s3.AmazonS3Client.invoke(AmazonS3Client.java:4365)

Does anyone knows how to connect to DocumentDB and other endpoints that needs SSL in a Java program?
I tried specifying the pem file on the MongoDB URI but the parameter ssl_ca_certs is not known by the driver.