If you need to send files to client working on svn, to reflect changes, for binary files (pdf, jpeg..), I would recomment to create dump, instead of diff, as the diff usually ignore the binary files, or during the load, the update is not properly done.
svnadmin dump c:\svnrepo -r revX:revY --incremental | svndumpfilter include project --drop-empty-revs > file.dump
If you need only specific projects, use the svndumpfilter
svnadmin dump c:\svnrepo -r revX:revY --incremental | svndumpfilter include project > file.dump
For the diff, use
svn diff svn://localhost/tag1 svn://localhost/tag2 > file.diff
For a diff, you first need to be in the project directory
D:\Projects\workspace\IDFactuBatch>cvs -d :pserver:username:password@host:/RepositoryPath diff -r rev# -r rev# > C:\test.diff