LaTeX amsbook compiles differently every time (almost!)

I translated a book and had it published, around 700 pages. When corrections were needed I re-ran the file and now every thing is different! In particular the number of words in a line and page break points are all different.

I use amsbook documentclass, MikTeX 2.9, Winedt and run the file using pdflatex on Windows 10. (What more info is relevant?)

Is there a way to get the same output as six months ago? If not I will work with pdf editors which are worse.

• the standard classes and ams classes have not changed in the last 6 months and haven't had any changes likely to affect line breaking in the last 30 years, so presumably you are using some package that has changed, add \listfiles do your document then look at the file list in the log for any new dates – David Carlisle Aug 14 at 9:18
• also if the text is not in English make sure your updated miktex has the relevant language support files installed/ – David Carlisle Aug 14 at 9:20
• If you use babel, the hyphenation pattern may have been updated. – Sveinung Aug 14 at 13:30
• How extensive were the corrections? Paragraphs that had no corrections should not be broken differently, but every change does run the risk of changes in the line breaking, and thus the page breaking. A change in number of words in a line implies that the margins were changed; the defined margins in amsbook haven't changed since the class was written (sometime in the 1990s). Is geometry being used, and if so, were the dimensions somehow changed? – barbara beeton Aug 14 at 22:41
• Thank you for the replies. However the situation is getting more mysterious: I found a copy of the whole directory of my book on my disk D. There I run the master file and get exactly the same output as the book. Then I run the master file on the directory in disk C and I get a different result. The most striking difference is that on disk C I get noticeably smaller fonts (palatino). (all runnings are done without any changes to the text yet.) – Sinan Sertoz Aug 15 at 12:07