Add identifier column before appending queries

Hi,

I'm bringing a PDF into Power BI that contains 3 tables that I would like to append to create one "master" table. All of the columns match up, and I can append the data as needed with no issue. However, I need a column in the new "master" table that identifies each row's source table.

I want to add a column called "Source" to the query for each of the source tables, of which every value will correspond to that source. E.g. the every value in the "Source" column in Table 1 of 3 will be "Table 1" etc. My thinking is that when I append the 3 tables, I will be able to differentiate which table the data originally came from using the "Source" column.

I'm relatively new to this, so I may be missing something obvious but I'm struggling to do this, as there doesn't appear to be a way to add a column with manual values to a table?

I should add that I can't add the identifying column before processing as I am not the publisher of the PDF, and it is updated weekly.

Example of the logic:

Table 1

Table 2

Master/appended table

Thanks