Hi Kerstin,
Instead of adding to Moodle as a Webarchive, use the File resource instead.
Enter edit mode in your course. Click Add and activity or resource. Scroll down and under RESOURCES select File then click Add. On the Adding a new file page, type in a name and description. In the Select files section, click the Add button. Click Upload a file then click on Browse. Navigate to your Tine file, select it, then click Open, then Upload this file. Back on the Adding a new file page, click on Save and return to course as the defaults for the other settings should be okay. Back in the course, click your new link to test it out.