When I export a PDF from InDesign, the file changes.

Hi ​@Dimitris35249630njuz, thanks for reaching out. We’re sorry you’re experiencing this issue.

In addition to the information requested by Manan and Creative Explorer, please share your version of InDesign and your computer’s operating system.

Please also share a screenshot of the Export Adobe PDF window so we can better understand the settings you’re using to export the file.

Thanks,
Nikunj

​@Dimitris35249630njuz By any chance do you have the original source file versus using the the PDF which may help the export issues that you are seeing? If there is no other file than a PDF, I would look to see if there was a transparency flattening that is the issue? 

Share more information what changes. Any screenshots to understand the problem better?