Are Material Orders and Orders related under the hood?If so, can you make Form Rule that shows button link when the lookup field has a value?Otherwise, it sounds like you'd want check out the Pipeline Search Records step in the Pipelines Channel to find the relevant records, then loop them (even if there is only one) and update the link value. Worthing mentioning that Formula URL field may be of use in conjunction with a stored ID to form a link to the Order. In other words, store the minimum necessary information, you likely don't need to store a full link, as the majority of the link will be the same in all cases, it's likely just the ID at the end of the link that differs (e.g. &rid=123)
But without understanding more about your schema, it sounds like this should be handled via relationships (with a lookup link) vs. Pipelines.