Hi @Hawk_Lee :
Taking into account your needs, I think that using different data sources has different advantages.
SharePoint- When you are generating HTML text, you can directly use the RUL of the picture
CDS- You can directly store the picture in the data source
Important: At first, glance does not seem to work as when viewed in a Model-Driven app the image is all black. What happens is that the pen input as default has a transparent fill color, which is not supported by CDS entity images. To make it work, set Pen input fill color to white or another color of your choice. PowerApps Pen Input – Have issues? Problem solved!
Considering the ease of use, I would like to introduce a method that uses SharePoint as a data source, but does not require flow to store pictures.
I’ve made a test for your reference.
using pen input for signature
My data source:test
step1:add a new mode form control(Form3)
set the attachment control’s items property to: MyPics /*my custom collection*/
set the attachment control’s Value property to:Value(advanced-DATA-Value)
You can refer to this case
step2:add a PenInput control(PenInput1)
Step3:add a button and set it’s OnSelect Property to:
ClearCollect(
MyPics,/*create a collection to save the pic*/
{
DisplayName: Concatenate(
"image",
Text(
Now(),
"[$-en-US]yyyy-mm-dd-hh-mm-ss"
),
".jpg"
),
Value: PenInput1.Image,
AbsoluteUri: "",
Id: "00000000-0000-0000-0000-000000000000"
}
);
SubmitForm(Form3);
Patch(
Test,
First(
Sort(
Test,
Modified,
Descending
)
),
{
signature: First(
First(
Sort(
Test,
Modified,
Descending
)
).Attachments
).AbsoluteUri
}
)
export form to PDF file which the signature was include.
Step1:Add a HtmlText control and set it’s HtmlText property to:
"<!DOCTYPE html>
<html>
<body>
<h2>PDF Report Example</h2>
<h2>"&First(Sort(Test,Modified,Descending)).Title&"</h2>
<div>"&"<img src="&First(Sort(Test,Modified,Descending)).signature&">"&"</div>
</body>
</html>
"

Step2:Creat your flow(follow this video)
I think this link will help you a lot:
https://blog.muhimbi.com/2017/08/convert-powerapps-data-to-pdf.html
Best Regards
Bof