Error trying to combine multiple PDF files: To view the Flash technology content [...]

If you are trying to combine them using Create > PDF Portfolio, that would cause this, as that method uses Flash, which of course is now obsolete.

You would need to use Create > Combine...

The current Acrobat creates Portfolios in a different way.

Hi there

Hope you are doing well and sorry for the trouble. As described you are unable to combine the PDFs and getting the above mentioned error for flash player

Is this a behavior with a particular set of PDF files or with all the PDFs that you try to combine? Please try with a different set of PDF files and see if that works.

What is the version of the Adobe Acrobat XI you are using? To check the version go to Help > About Acrobat and make sure the application sis updated to its last version 11.0.23 Go to Help > Check for updates and reboot the computer, you may also download the path manually from the link https://www.adobe.com/devnet-docs/acrobatetk/tools/ReleaseNotes/index.html

Note: Adobe Acrobat XI is an EOL application for more information please check the help page https://helpx.adobe.com/acrobat/kb/end-of-support-acrobat-xi-reader-xi.html

You may try to combine the PDF online here https://documentcloud.adobe.com/link/acrobat/combine-pdf  and see if that works for you.

Regards

Amal