Since today all MS Office files (Word, Excel) are open in the word Client application as Read Only mode, if I visit the SharePoint via https. If I Change the URL to http instead the Office files can be edit in word/Excel.
The HTTPS certificate is self signed but the certficated is added to the trusted certifcate store.
Any ideas why this happend? I think it is related to this Office security patch, because there is this Paragraph in the description: "This security update resolves a security feature bypass vulnerability that exists when Microsoft Office does not validate URLs"