You can not convert a pdf file into a .tax2019 file. In you used the Online version you can download the .tax file.
You should always save both the PDF file and the tax data file each year so you have a copy when you need it or if you ever need to amend it in the future. You shouldn't rely on getting a copy from Turbo Tax.
Save the PDF
https://ttlc.intuit.com/community/saving/help/how-do-i-save-my-turbotax-online-return-as-a-pdf/00/26...
Save the tax file
https://ttlc.intuit.com/community/saving/help/how-do-i-save-my-turbotax-online-return-as-a-tax-data-...
Why doesn't that link work for you?
