What does "application LibreOffice can't be opened mean" when opening Libre

number 1712 is shown

What operating system and version of LibO are you using. This helps us answer a question. But:

You may find ask.libreoffice.org/en/question/48754/i-get-error-1712. helpful. I assume you are using an Apple Mac and this is a Mac error. It appears to be a timing problem. The previous answer says:

Are you using a Mac? I’m not a Mac user, but a quick Google tells me that the error is commonly a Mac error, and to do with timeouts.

Close LibreOffice and try to copy the file to another location before trying to open it. If you get an error during copy, the file might be corrupt or the hard disk is having problems. An issue outside of LibreOffice in other words.