Hi @werner1 ,
Do you want to insert a Line Chart into a PDF report using PowerApps app and MS Flow?
If you want to insert a Line Chart into a PDF report using PowerApps app and MS Flow, I afraid that there is no way to achieve your needs in PowerApps currently.
I agree with @mdevaney 's thought almost. Currently, as an alternative solution, you could consider draw your Line Chart in Power BI Report, then you export the Power BI report into a PDF.

On your side, you could consider add your data source as dataset into your Power BI/Power BI Desktop, then add a "Line Chart" visual into the Report panel, then configure the Line Chart based on your dataset. If you create the report using Power BI Desktop, please publish it to your Power BI service firstly, then export the report into a PDF file.
More details about exporting Power BI report into a PDF file, please check the following article:
https://docs.microsoft.com/en-us/power-bi/consumer/end-user-pdf
Best regards,