… editing the parts with the Document Tool is a problem …

I have never heard of the Document Tool.

What is the Document Tool?

Do you perhaps mean the Expression Tool?

… Every time I reopen the file or save it as a PDF, layout has changed. Names of the movements, system breaks, rehearsal marks, number of measures in a staff: changes made with Selection, Text or Page Layout Tool don't stay where or like I leave them …

I have downloaded your Finale document.

But I have not been able to reproduce your problem.

1) I opened your document, and examined the Violin I part.

I closed the Finale document, and opened it again.

The Violin I layout had not changed at all.

2) I opened your document, and examined the Violin I part.

This time I saved and closed the Finale document, and opened it again.

The Violin I layout had not changed at all.

3) I opened the document, and examined the Violin I part.

This time I exported the Violin I part as a PDF file, and closed the Finale document, and opened it again.

The Violin I layout had not changed at all.

Can you provide steps to reproduce the problem?

Thanks, Peter, for your comment. 

I edited the parts through Document>Edit Part. All the parts had measure numbers when a system beginning had a rehearsal mark. The titles of the movements were conceived as center headers. Part 2 (Wals) began at page 2 (strings) through a page break, measure 9 was a new system. Everything vanished or changed at reopening or saving as a pdf. You can see it's a mess.

I tried to make two examples to show you the difference, but when I saved the document under another name (Example 1) the problem seemed to be solved.

However, for now I think it's safer to use the Extract Parts method to edit the parts.

Kind regards,

John