Why some pdf file miss some content open with Adobe Acrobat 8.0 ?But the same PDF file open by Adobe DC reader can display all content.

Without seeing the PDF file in question it's impossible to say why this is happening. There are a number of possible reasons:

If the file was generated with an Acrobat version that is newer than Acrobat 8, it's possible that the file uses some extensions to the PDF-1.7 format that were introduced after Acrobat 8.

It is possible that the file is corrupt, and a newer version of Acrobat/Reader has ways to deal with this particular problem.

It is possible that a bug in Acrobat 8 is not showing the content in question, but a newer version of Acrobat/Reader will display the file correctly.

There are probably more potential reasons than these, but again, without actually debugging the problem with access to the file, it's impossible to say what exactly is going on.