Cannot open text document

I cannot open an important text document that I created in Libreoffice and saved as docx.

I get the following error message:

File format error found at SAXParseException: '[word/document.xml line 2]: Attribute w:cstheme redefined ', Stream ‘word/document.xml’, Line 2, Column 72562(row,col).

It’s an assignment that took me 3 days to put together and I really don’t want to have lost it!

Does anybody have any idea whether and how I can retrieve it?

docx is a Microsoft Word Open XML Format Document file format - I use it when I share Libreoffice files with non odt-users.
Thanks for your suggestions to try and change the name via File Manager (Finder in my case - am a Mac user) but unfortunately that hasn’t made any difference. But I can see that I’m definitely behind with my LO update so will get on to that straight away and keep all fingers crossed that might help…

To update, mine is in help, pull down. it updates by a couple of clicks. Hopefully yours is like that. Also, try opening it in a simple text editor or if possible adobe. Then Ctrl A to copy all, paste to a new file. Odd but has worked for me.

Also, there are sites that coverts files to whatever you want! Google convert a file. good luck. i know the feeling.

OKay, the LO update has at leas allowed me to open the document albeit a warning of it possibly being corrupted and crashing the system. But I’ve lost about 1/3 worth of content and quite a bit of my formatting. But at least it’s better then nothing…

Good to hear! Just thought of something! LO saves file in “user” folder in background. It backs up I think every 10 minutes by default. I changer mind to ever half hour. I have never tried to retrieve a file there before, but path is at, path is shown in pull down, Tools-Options-LibreOffice-Paths! C:\Users\Administrator\AppData\Roaming\LibreOffice\4\user\backup… Open this through LO, “open”.

I’m not sure what docx is. But I would open file manager. if in windows, windows explorer. And make a copy, so you have 2 until ya get it fixed. Save one, play with the other. Try renaming one to _.doc… ("" meaning a the name it is, then .doc) Why the “x”? May not work, but it’s a start. I just made a file.docx. Iy reopened ok. I’m using LibreOffice 5.3.4.2. Maybe update?