How to import PSPICE Model into Orcad Capture?
The answer below is how to properly import a PSpice model (usually generated in a third-party software) into Orcad Capture and PSpice so that both the schematic editor and the simulator work without errors.

Summary
Firstly, the model must be imported into Orcad Capture (so that a new component and a new library .olb is created. Secondly, the model must be properly "fed" to PSpice.  

Step 1. Creation of Orcad's component library (.olb file)  


Open Orcad Capture -> File -> Import -> PSpice -> OK  


  

Notes:
a) Field Open: path to the PSpice model
b) Field Save as: path to an Orcad library to be created with a new component. Extension must be .opj
c) Field Schematic Configuration File: leave it as suggested  

Step 2. Setting up PSpice simulator  


Copy and paste your model file (e.g. Model.mod).  
Rename the file from Model.mod to Model.lib. This is done, because PSpice works only with .lib extension.  
Open Orcad Capture, PSpice -> New Simulation Profile -> Enter any name for the profile (e.g. tran1) -> In an opened window go to "Configuration files" tab -> Library category


  


Enter the path to Model.lib in the Filename field -> Press Add to Design button
Make sure that the file {Orcad installation directory}\tools\pspice\library\nom.lib is also added to the Configured Files as a Global
Make sure that in the Library Path there is a correct path to the PSpice main library (see the picture above as an example of a proper path).  


Final comments
a) Wrt the error you mentioned "ERROR(ORPSIM-15108): Subcircuit LM741/NS used by X_U5 is undefined", this is caused by improper setting of PSpice simulation profile (either improper path to the Model.lib or main Library Path).
b) Overall, the trick is that import of a PSpice model is done twice: once in Orcad Capture and once in PSpice (would have been better if done automatically by the program).
c) Of course, to add the component in Capture, one needs to add the library (Model.olb) in a Place Part subwindow.
d) Not sure, but likely names of the files Model.lib and Model.olb must be the same, so that PSpice knows what Spice model to use.