Sorry you are having problems.
You haven't given us enough information to offer any advice. Here are some basic questions for you.
Operating System Platform and Version?
SmartOffice 2 release (current release is 2.3.16 for iOS and 2.3.10 for Android)?
Where did you acquire your copy of SmartOffice?
Document location (MyDocuments, Dropbox, Box, Google Drive)?
Then we could use some information about other behaviors:
Can you open other document types (XLSX, DOC, DOCX, PPT, PPTX, PDF)?
Did you create this this document on the device, or is it a document created elsewhere and shared with you?
Can you email the document, even if you cannot open it?
Did anything change in your operating environment?
Did you upgrade your device operating systemanything recently?
Can you upload the document(s) here?
SmartOffice Support Team