Is it legal to use an agpl v3 app in a closed source web app?

Question

Licenses for software and other works

There is onlyoffice document builder program . It allows you to programmatically generate office documents and pdf. They have the following on their website:

By complying with the terms of the GNU AGPL v.3 license , you can use the open source ONLYOFFICE solution available on GitHub . To protect your intellectual property and receive professional technical support, you must purchase a commercial license.

It is intended to use this program as is. No changes to the source code are expected.

It is supposed to programmatically generate a text file with builder commands, and then call this application in the console, feed it the generated file and get the result.

It is not supposed to use the builder's source code in the web service code.

It is clear that this application can be used for commercial purposes. It is not clear, however, with such use, does the license require to open the source code of the web application? I haven't found a definitive answer on the internet yet.

I am very confused by the phrase "to protect intellectual property".