WHT has nothing to do with this. There is never tax in Estonia, once CIT has been paid (unless there is some sort of special exception due to the other country being considered a tax haven).
As
@marzio explained, you can avoid the WHT by putting a holding company from a country that doesn’t charge WHT in between you and the Romanian company. Within the︀ EU, there is never WHT between companies and their parent companies (parent-subsidiary directive), but there︁ can be WHT between companies (including holding companies) and their individual shareholders.
Countries that don’t︂ charge WHT and this should be a good choice for a holding company include Estonia,︃ Cyprus, Latvia, probably others.
For the choice of a holding company, see this thread:
https://www.offshorecorptalk.com/threads/holding-for-assets-in-germany-eu.30839/
Estonia is nice and simple for a holding company, but you will have to pay︄ 20% tax if you sell the operative company (subsidiary). So having the holding company in︅ a different country might be preferable, unless you are sure that you will never sell︆ the operative company.
The term you are looking for here is the participation exemption. Estonia︇ has no participation exemption for the disposal of qualifying shares, most other countries do.
The critical thing here is that you don’t manage the Romanian company from Estonia and that︈ there is substance everywhere. Please don’t do anything like this without consulting with the proper︉ lawyers from all countries involved. I have not done this myself - I only discovered︊ that it should be possible in theory. There will be many pitfalls you need to︋ avoid.
If you get the green light from your lawyers, I’d be interested in hearing︌ about how you set everything up in the end.