Hi Martin thanks for posting in the community!

We currently support diagram imports from Visio Gliffy Draw.io and OmniGraffle. We also have a PowerPoint Add-in for inserting diagrams from Lucidchart into PowerPoint. You can find more information in this Microsoft Integrations article from our Help Center. 

As a workaround you could export the your PowerPoint diagram as an image and insert it to Lucidchart. However we're always looking for ways to improve. If adding the ability to do this would be useful for you please let us know in the product feedback section. 

Thank you and please let me know if you have any questions!