I'll use this file as an example: (Yep, there are others...)

I don't mind exposing this one to the world...as it doesn't contain sensitive information. The only difference is, the file in question has 1 and 1 vs 1 and 2 in the 2nd column. How is a hidden file locked? A file (I don't think) I had access to...

.pmdx is a PageMaker file. SoftMaker is the company that makes the software. May or may not be compatible with current Excel format, (as far as I can tell.) Your mileage may vary. (As they say.)

Thanks.

I think you mean the default location of the lock file is in the same directory as the actual document file you are trying to open. Since the OP is trying to open the file with different software and they have default lock file names its probably due to something else in common.

Since the OP mentioned opening the file from a web browser link the default lock file location can not be in the same directly since it does not exist on the system. I did find the following thread which appears to duplicate the OPs problem and due to the office programs not having write permissions to the web browsers default temporary file location. This would makes sense as being only a linux problem.

https://forums.linuxmint.com/viewtopic.php?t=347810

Addendum to my previous post... A lock file is a temporary file that is created when a document is opened to prevent other users or yourself from trying to open the file for editing twice. It should be automatically deleted when the document file is closed but sometimes for whatever reason that does not happen. In that case you need to manually delete the lock file.

It has nothing to do with the actual unix file permissions.

Sorry, I should have mentioned that. The other difference is, xlsx in both cases, as you see above...And will open as a read only file...i.e. the software, and file format are compatible. The hidden file is just locked, just like above.

The hidden file is actually the lock file.
If you remove the lock file for the one(s) you are having an issue with then it should open normally the next time you try.

Lock files may be left behind if you have the file open for editing (as one example) then restart the system or do something else that caused the editor to disappear while the file is still open. It can (and sometimes does) also happen if you are working with a file on a remote system and for some reason your connection gets broken while the file is still open.

The first file looks like a lock file.
Slightly different naming than what I showed you, but then maybe a slightly different software made it.
Remove it or rename it, see if that solves the problem.

I was able to Copy the Original, Rename the Copy, and Delete the Original. That worked.

In that case probably you can mark the thread solved.