Assistance Required: Uploading and Replacing Modified PDFs in Windchill EPMDocument Attachments via

The PDFs are sent to the attachment section. For example, there are four PDFs created in sequence, but later a user inserts a PDF between them, for instance, between 1 and 2, and assigns it a sheet number of 2. However, because it was originally a PDF with a page order of 5, it naturally appears at the end instead of between 1 and 3. I developed an intermediate application in C# that scans the incoming PDFs using OCR, rearranges them according to the sheet number, and converts them back into a PDF. However, I couldn't find an API that allows me to upload this modified PDF back into Windchill. How can I send or replace this modified PDF in the Attachment section of the relevant drawing in EPMDocument? I couldn't find a way when I looked at the REST APIs in WRS. Could you help with this?