Last Update: 5/8/2019
First, you must bring both graphs into the same project. and there are two methods presented here. Read through each method and decide which one you prefer. Then, read through "The Final Step" to complete the merging of the graphs.
You may want to read FAQ-427 How to bring in data from another Origin project?
Open your two projects in two Origin. In one Origin, in Project Explorer, choose the folder which includes the graph, right click and choose Copy from context menu. Next, go to another Origin, right click on one folder and choose Paste from context menu. This first folder with all its worksheets and graph windows will added as subfolder in the Second Origin.
Open one of your projects, activate a Graph window and select File:Save Window As to save the Graph window as an OGG file for later use. Repeat for each Graph Window of interest and for each Project file. You can open these OGG files into any Project by using File:Open and selecting OGG from the Files of Type drop-down list.
Now that the windows are in one project, you can merge your graphs onto one page by select Graph: Merge Graph Windows.
By default only graphs in active folder will be shown in the Merge Graph Windows dialog. You can choose the triangle button next Graphs box to add graphs in different folders