disable pdf preview in mail

Hello,

I'm experiencing a weird behavior in the mail app (the apple one) of my iPhone 6s. I'll try to explain the best I can.

Until yesterday, all the pdf files I received in my iphone's mail, were showed like a clickable square that opened the file's content. But now, all the pdf's are "previewed" like a normal image (as if they were a jpg or so) and I cannot click them and work with them anymore. If I long press the preview, the only option that show up is: "open as image", but not as pdf file.

Isn't there an option like "open with" to restore the normal mail behavior? I've spent a couple of hours with the phone and searching in the internet, but I didn't come up with any solution. I hope that resetting the phone isn't the only one solution.

Thanks a lot for your help and excuse me for my lame English.

Best regards.