How to obtain a readable format of an article? It became a real problem for me. I need to read some old articles for my research but these qualities are so bad that I can't even read the text. For example, this article "https://www.sciencedirect.com/science/article/pii/0012365X74901368?via%3Dihub".

Do you have any opinion on my problem?
You have two options. Either you try to locate a paper copy (or a copy thereof) of the journal issue via your local library and if necessary via the interlibrary loan or you contract the vendor of the digital copy (sciencedirect in your case) and complain about the quality of the digitised paper asking them to upload a better-quality version. I tried this with another publisher (degruyter) and it took a couple of months before they updated the digital copy of the paper on their website.