linux find by file extension code example

Example 1: how can I find perticular extension in ubuntu?

find . -type f -name "*.txt"

Example 2: terminal find file by extension recursive

find /directory/path -type f -name "*.in"

Example 3: linux find file

# syntax 
# find *</path/to/dir> '(' *<Filter-1> *<and/or-operator> *<filter-2> ')'

# example 
find . '(' -name "Test*.pm" -a ! -name 'Useless*' ')'