You can use BarSeries with set Y0 and Y properties in order to draw them starting at specific point - similar to How to: Create Range Chart (the example uses ReaSeries that can be replaced by BarSeries). The attached demo report illustrates such settings. It is a TRDP file that can be previewed in the Standalone Report Deisgner of R2 2017 and newer.
already existing PDF files cannot be merged in Telerik reports. You can use third-party libraries like Telerik Document Processing Libraries to import and merge PDF files of different sources - Telerik Document Processing: PdfProcessing.
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