Hi @Timfl. Thanks for being part of GoDaddy Community!
A server-side include (SSI) should work within Plesk, but you may need to take these steps to get it to work for HTML files specifically. Hope that helps. If not, feel free to provide more information. Others in the community may be able to provide you with additional suggestions.
JesseW - GoDaddy | Community Manager | 24/7 support available at x.co/247support | Remember to choose a solution and give kudos.