It's a little intimidating to get started with an XML parser, so Here is a working solution for the text you presented:

Please use it as a model to learn how to use the XML parser for your real life problem.

$ perl -MXML::LibXML -e '
my $dom = XML::LibXML->load_xml(string => shift);
print $_->to_literal(),"\n"  for 
       $dom->findnodes("/collection/document/*/text"),;
'  "<collection><document><title><text> Hello how are you</text></titl
+e></document><document><abstract><text>I am fine</text></abstract></d
+ocument></collection>"
[download]

Output

 Hello how are you
I am fine
[download]