i am not able to export my projects as when i open the file on acrobat reader or microsoft word it shows that this file is either decoded or something like that please help
Welcome to the community. Project file/aia is a zip type file and can be extracted with 7zip or winrar or a similar program (this is used in special occassions).
Aia files can not be opened and edited by a program in your pc, only at ai2.appinventor.mit.edu .
Same thing for app/apk files, can not run in pc unless you have an android emulator
In order to save project see
The Blocks Editor has a feature that lets you Download Blocks as Image if you want to show others parts of your app in a document. I do it for procedures and events in my sample apps.