Equations as "picture"

so sometimes I open a document and previously entered equations are just pictures, as in I can’t edit them anymore. double clicking on them doesn’t allow me to edit them, also from Edit → objects is grayed out which should allow me to go Edit → objects → edit

so I’m wondering how I can avoid this.

System: Ubuntu 16.04 64bit

These “equations” most likely were not created with ‘Math’ (but probably with Word / MathType). Since different formula editors are not expected to be compatible, you will see a kind of preview image of the formula that was created with the alien software.