My process begins with creating invoices in our ordering system. These are saved in a specific file. I found opening in 'Preview' rather than using Adobe simpler and easier.

I would then name it, and it used to use my default file so I always knew where it was saved.

Now, no matter what I do, it will not use my default file (see: 'where'). It will only create a file showing there as printing.40573.1 which, if I forget to use the pull down menu to chose my usual file, will 'go away' and searching cannot find the document, and the 'printing.' number will change every time. At that point it's easier to just do it all over again.
I did originally try to 'Save as pdf' which does seem to remember the default file I use, but for whatever reason it won't let me 'paste' invoice numbers. Invoice numbers can often be long and complicated so in order to record the invoice number accurately it is much safer to copy and paste rather than typing it in every time and possibly mistyping. So I developed the process using 'open in preview' which does allow pasting.
So your suggestion of 'try something different' was already tried and rejected well over a year ago.
I know it doesn't seem like much, but I'm not sure why this update has made the process less simple.
I simply want to be able to designate a default file for saving documents when I open in Preview.
Is this possible?
Thanks again.