My png images are offered for free download without Adobe watermark at https://clipart-library.com/ I only upload to Adobe.
What can I do?

Send a DMCA takedown notice to [email protected]

Quote from: Her Ugliness on October 19, 2023, 09:34
Send a DMCA takedown notice to [email protected]

Thank you for advice. Do we need to copyright our artwork ourselves or it is automatically copyrighted by Adobe with copyright office?

Before you get too upset about clipart-library, try to download one of the images.  You'll find most of them are just the thumbnails from stock sites.