How to get portion of lines from all .txt files in a directory?

I have 5,000 text files of journal article citations. I am trying to extract only the abstract portion. Meaning that I want to keep the same text document and delete all the other text except for abstract. I am very new to Linux and I have been trolling your board for a while.

how to extract words that after keyword

execute command on all file in a directory

for file in test
nano my.sh
while read variable do
  sed '0,/^Abstract$/d' 
done <file

Here is an example of a file its similar to a scientific journal article

Sponsor     : Beckman Res Inst Cty Hope
      1500 E. Duarte Road
      Duarte, CA  910103000    /   -

NSF Program : 1114      CELL BIOLOGY
Fld Applictn: 0000099   Other Applications NEC                  
          61        Life Science Biological                 
Program Ref : 9285,
Abstract    :

          Studies of chickens have provided serological and nucleic acid                 
          probes useful in defining the major histocompatibility complex                 
          (MHC) in other avian species.  Methods used in detecting genetic               
          diversity at loci within the MHC of chickens and mammals will be               
          applied to determining the extent of MHC polymorphism within                   
          small populations of ring-necked pheasants, wild turkeys, cranes,              
          Andean condors and other species.  The knowledge and expertise                 
          gained from working with the MHC of the chicken should make for                
          rapid progress in defining the polymorphism of the MHC in these                
          species and in detecting the polymorphism of MHC gene pool within              
          small wild and captive populations of these birds.       

Thanks to KasiyA and John1024 I now understand how to get portions of lines from a directory. Here is how you do it for sub directories

find -name *txt -type d -exec sed -i '0,/^Abstract/d' *.txt {} \;

For more details about the find command click HERE OR this link from stackoverflow Here