2018 was one of those unusual years (like 2020 is now)
1) the PDF you prepared and printed right after your file was accepted is likely the correct one. This step is critical to be done by everyone, and you did that part correctly. Always create a separate PDF copy right after filing and acceptance.
2) IF you ran any TTX software updates , after that acceptance date, there could have been changes implemented in the software that changed some lines/fields and the resulting refund, or owed $$ amounts. Thus opening the .tax2018 datafile after an update has been done, may result in differences in your file when opened again. Many of us lock-off our updates right after filing to prevent that from happening so that we can always see what we originally filed. (I update and check my file on a separate laptop installation first, then only update my main desktop computer if my tax file doesn't change on that separate TTX installation. ) Of course, a new installation of the software done now will contain every update, including any issued long after you submitted your original file.
3) For 2018 taxes, the IRS made an unusually late calculation change that affected some people (I seem to recall it was even after AFTER the April filing deadline . The change was on the Schedule D tax calculation worksheet... It made me owe them $7 more, but I've ignored it so far). But if you filed before April of 2019, or updated or re-installed your software sometime after April 2019, that might be why opening your .tax2018 datafile now, doesn't match exactly what your as-filed original PDF shows.
4) Creating a new PDF now, and examining values on the lines, may show you what has changed between the two filings, and might lead you to the reason for the difference...one hopes it is a minor one.
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5) I hope you did not do this....but Some people see a change, because they experimented later with their original tax file.....never do that...only mess with a "copy" of the original.
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*
