We tried the same at our end and unable to reproduce the same.
In order to open an Excel document( attached as an attachment) you should have an application installed in your mobile device that supports the .xml files.
Similarly if its an pdf attachment attached to the pdf doc, then that should open up through the Adobe reader itself.
Adobe Acrobat Reader mobile application is already compatible with mobile devices, there isn't anything specific needs to be done.
What about attachments as annotations within a PDF?
I noticed that on iphones, the annotations will not even appear.
Are you experiencing this problem with a particular document?
If possible, please share the document with us we would like to test it our end to see whether its a problem with the file or application itself.
I have shared the email address via private message. kindly send the sample file to us on that.
Once you open a document with an attachment like this in the Acrobat iOS or Android viewers, you can tap on the document and then tap on the attachment (paperclip) icon in the toolbar.