Always work with your files in the native ODF fileformats, always save your important document into the native, standardized ODF formats (.odt, .ods, .odg, .odp.):
- if you want to work efficiently with Apache OpenOffice or LibreOffice.
- if you must edit the saved documents again in the future.
Maybe those Equations was saved as pictures in the foreign MS fileformat. The binary file formats (.doc, .xls, .ppt ) never was standardized, but the ODF is an International Standard.
You can EXPORT a copy into the foreign formats at the end of editing, but the MS-type copies will have not 100% compatibility.
Can you upload your example file here?
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And your signature shows me a quite old version of the OpenOffice.org software:
OpenOffice.org 3.3 Mac OSX 10.6.6
You must upgrade your software, and/or update your signature.
The latest version of the Apache OpenOffice is AOO 4.1.1,
the latest "Still" version of the LibreOffice is LO 4.4.5
and the "Fresh" version of the LibreOffice is LO 5.0.2
Just a tip:
The LibreOffice have more compatibility with the MS fileformats, but it never will 100% of compatibility.