Attempt to open Word docs in Pages - file format invalid

Pages must translate any opened Word document into Pages internal (.pages) document format. Pages v13.1 (last compatible for Monterey) on Monterey 12.7.3 is no exception. However, if the contents of that Word document cannot be translated, or it is in a (renamed) file format that Pages cannot open, you will likely get the file format invalid dialog.

One can open some of these invalid files in LibreOffice, and then resave by another name as a Word .docx and those will open in Pages. I haven't used OpenOffice in over 12 years as it has fallen behind LibreOffice in capabilities and updates.

Unless something has "damaged" the remainder of your Word documents, Pages should open and translate them.

Pages document format can only be opened by Pages whereas Word documents can be opened by most modern word processing applications. Converting them to Pages is painting yourself into a corner of platform incompatibility. Just as Pages translates the Word document on opening, it must translate it again to export to Word, and Apple does not guarantee translation in any direction.

Are these older Microsoft Office documents?

LibreOffice can open and convert Microsoft Office documents to newer Office formats.

That’s been useful when Office itself couldn’t open the Office document, and should work here as well.

Newer Microsoft Office documents are represented by ISO standards and the LibreOffice/OpenOffice OpenDocument formats by different ISO standards. In a nutshell that means that most third-party word processing, spreadsheet, and presentation applications are designed to open Microsoft and sometimes both standards documents. Both LibreOffice and OpenOffice are Microsoft Office suite clones and do both document standards.

Apple's Pages, Numbers, and Keynote represent Apple's own, proprietary document standard and only Apple's applications can open their own documents — and then it will depend on the age of those documents, and the version of the applications. Apple's applications can potentially open Microsoft Office documents read-only if they are not damaged, not too old, or do not use Microsoft features that Apple's translation process was not designed. And, because Apple's applications are not clones of Microsoft applications, you can never be certain if they will translate correctly in either direction.

If you are not sharing your Microsoft documents with anyone, then it is your call whether you use Apple's Pages, Numbers, and Keynote to perform document transformations into a proprietary format.

You can choose to use the free LibreOffice, or continue with OpenOffice as they are free applications and supported on macOS Catalina and later. There are paid third-party MS Office clones that are quite well done that can open Microsoft documents in their native format. SoftMaker has Office 2024 for Mac. I don't benefit from mentioning this vendor.