Historically, Lertap 5's main focus has related to the application of "CTT", classical test theory. But it certainly has support for IRT users, to be sure: see this 2015 document.
An option in the System worksheet to turn on "experimental features" will get Lertap 5 to add three columns to one of its standard reports, "Stats1b". These are the "bis.", "b(i)", and "a(i)" columns seen in the screen snapshot below:
a(i) and b(i) are estimates of the 2PL IRT parameters, while bis. is the biserial correlation coefficient. The derivation of these statistics is the focus of this paper.
Lertap 5 has extensive, well-developed support for users of ASC's Xcalibre IRT program, and it will also output data ready for input to Bilog-MG. (The data file made for use with Bilog-MG has a format also useful to quite a number of other programs, such as ConQuest and RUMM.)
A webpage which demonstrates the strong relationship between CTT and IRT statistics is available at this link, and a technical paper, somewhat critical of the Rasch model, may be found by following this hyperlink. Remember to take in this 2015 document when time permits, a document having the very latest on IRT developments in Lertap 5.