Here is a quick guide to convert your pictures in PDF.

First, add a picture or a folder clicking the top left side button:
(You can use the drag & drop too)

Name:  Picture1.jpg
Views: 1232
Size:  10.7 KB

When you are ready, click on Next at the bottom (or on Options)
Click on "More Options..." to see all tabs available as below and select "Create PDF
Name:  Picture2.jpg
Views: 1183
Size:  18.8 KB

The PDF tab will appear:
Name:  Picture3.jpg
Views: 1126
Size:  15.5 KB

Now you can choose the output page size among existing profiles or create your own selecting "Custom". You can either choose "inches" (in) or "centimeters" (cm).
Name:  Picture6 .jpg
Views: 2529
Size:  47.3 KB

Below a few samples of different sizes:
Name:  Picture5.jpg
Views: 1109
Size:  14.7 KB

Eventually, click on Process to create your PDF file!