iPad Preview app not attaching PDF to Mail after signing

Every month I need to send an invoice to my customer. I create a PDF on the Mac, open it on my IPad (since IPadOS 26 using Preview app) and sign it on the IPad. I then use "Share ..." and select "Mail" to send out the document. The problem is: a new Mail window shows, but the document is not attached. Just missed a deadline because I didn't notice and the document was missing. Anyone else experiences this? IPadOS 26.0.1.

[Re-Titled by Moderator]

Original Title: Using the Share button on IPad Preview App does not attach the document to the mail