The answer depends on where your file is located. If it is stored on a Amazon S3 bucket for instance, you can create a connection to Amazon S3 and then define a dataset that refers to this file.
A the moment, the only ways for you to process this file are if it is in an S3 Bucket on AWS or if you use the little trick I demonstrate in this blog (https://www.talend.com/blog/2019/06/19/creating-avro-schemas-for-pipeline-designer-with-pipeline-des...). There is a "Test Connection" Connection Type which will allow you to create a manual Dataset. You can copy and paste your file contents into that Dataset and try out processing the data in your file from there.
I know this is not ideal, but Pipeline Designer is very new and is growing.
