[scotty1024]

You need the following includes:

#include <liberdm/erdm.h>
#include <liberipc/eripcviewer.h>
#include <liberipc/eripctoolbar.h>
#include <liberipc/eripcbusyd.h>

The following globals

erClientChannel_t erbusyChannel;
erClientChannel_t ertoolbarChannel;

This bit of code turns off the LED.

    // Turn off busy LED if we were invoked via [SHELL]
    erIpcStartClient(ER_BUSYD_CHANNEL, &erbusyChannel);
    busySetBusy(erbusyChannel, ccBusyState_Off);

This bit of code enables and then pops up the keyboard.

    erIpcStartClient(ER_TOOLBAR_CHANNEL, &ertoolbarChannel);
    tbSelectIconSet(ertoolbarChannel, ER_PDF_VIEWER_UA_ID);
    tbClearIconSet(ertoolbarChannel, ER_PDF_VIEWER_UA_ID);

    // Turn off trashcan
    tbAppendPlatformIcon(  ertoolbarChannel, ER_PDF_VIEWER_UA_ID, iconID_trashcan, -1);
    tbSetStatePlatformIcon(ertoolbarChannel, ER_PDF_VIEWER_UA_ID, iconID_trashcan, iconState_grey );

    // Enable then pop up keyboard
    tbAppendPlatformIcon(  ertoolbarChannel, ER_PDF_VIEWER_UA_ID, iconID_keyboard, -1);
    tbSetStatePlatformIcon(ertoolbarChannel, ER_PDF_VIEWER_UA_ID, iconID_keyboard, iconState_selected);

This bit of code labels the main window so Matchbox treats it as a Dialog and lets it set its own size (and brings it to front).

Atom window_type = XInternAtom(r->Xdisplay,
                               "_NET_WM_WINDOW_TYPE_DIALOG",
                               False);
XChangeProperty(r->Xdisplay,
                r->TermWin.parent,
                XInternAtom(r->Xdisplay, "_NET_WM_WINDOW_TYPE", False),
                XA_ATOM,
                32,
                PropModeReplace,
                (unsigned char*)&window_type, 1);

This bit of code flashes the screen black to do as ghost-less a refresh as possible

    // Full Refresh, chase off all the ghosts
    dmDisplay(dmCmdPriorUrgent, dmQFull);

This bit of code refreshes the screen without the black flash. It works much better for UI work such as that in mrxvt.

        dmDisplay(dmCmdPriorUrgent, dmQTyping);

To make the keyboard go away when you are done with it (or exiting mrxvt).

    extern erClientChannel_t ertoolbarChannel;

    // close keyboard
    tbSetStatePlatformIcon(ertoolbarChannel, ER_PDF_VIEWER_UA_ID, iconID_keyboard, iconState_normal);

And to link you need the following libraries.

-lerdm -leripc