How can I convert this RSA public key: 109120132967399429278860960508995541528237502902798129123468757937266291492576446330739696001110 6039072308886100726558188253585034290 57592827629436413108566029093628 2126359538366865626758497206207862794310902180176810615217550567108238764764442605581471797071 19674283982419152118103759076030616683978566631413
to *.pem file?
A "pem" file is not really a format, and different kinds of objects may be be stored in things called "pem" files. Most often these files contain either a base64-encoded X509 certificate or else a base64-encoded private key object.
Assuming you want an X509 certificate, you should next realize that a certificate consists of many fields, only one of which is the public key. So would need to decide on the values of the other fields. Finally, a certificate must be signed, with a private key.
PS. An RSA public key consists of a modulus and a public exponent. What is your public exponent?