HI am creting topics in DITA 1.3 framemaker. AM changing fonts in master page and clicking on update all. When i reopen the file next time the previous which i have applied does not appear any more.

If you're working on XML files, you can't change formatting properties on master pages or elsewhere and expect it to "stick". This formatting is applied by the structure application's template file. You'd need to make these changes to that template file, and then when you open an XML file using that structure application, the formatting is applied.

The default structure applications are installed here ..

     C:\Program Files (x86)\Adobe\AdobeFrameMaker<VER>\Structure\xml

Note that before you start modifying the default structure applications you should always create a backup of the originals. I recommend creating a "clone" of the apps that you're working with so you can switch from your custom app to the default app easily .. because you'll likely break something (everyone does).

If you're not familiar with structure applications or templates, read the documentation before going any further. Here's a blog post I wrote a while back about the different files that make up a structure application ..

     http://blog.leximation.com/2012/01/framemaker-edd-template-rules-–-what-is-all-that-and-how-does-it-benefit-me/

Cheers,

...scott