Challenge solved on June 20th, 2020. I enjoyed it a lot!

src/main.py

@@ -1,9 +1,19 @@
 # Resolve the problem!!
 
+import re
+import os
 
+current_dir = os.path.dirname(os.path.realpath(__file__)) #Get the current dir: https://stackoverflow.com/questions/5137497/find-current-directory-and-files-directory
+filepath = current_dir+"\encoded.txt"                     #Please make sure that the file encoded.txt is in the same dir.
 def run():
     # Start coding here
-
+    with open(filepath, 'r', encoding='utf-8') as f:
+        content = f.readlines()
+        str_text =''.join(content)
+        answer = re.findall("[a-z]", str_text) #The atribute re.findall returns a list and only works with the RegEx and an string to be parsed 
+        answer_str = ''.join(answer)           #https://www.w3schools.com/python/trypython.asp?filename=demo_regex_meta1
+        print(answer_str)
+    f.close()
 
 if __name__ == '__main__':
     run()