Might be better to provide a downloadable executable instead of asking the user to trust that the browser isn't doing what the browser was designed to do.
I plan to build a Chrome extension and am considering making it paid, around $2 for lifetime access. Also Desktop app is also good idea
Disagree, no way I'm downloading an executable from something unknown to modify a pdf.
I can easily check network monitor in the browser to see exactly what a web app is doing.
Running an executable is a risk by default and the way it interacts with my network is way less transparent. I honestly prefer this in the browser.
I disagree on that. I think that the main value of this kind of tools is "no installation required".
There are already free PDF editors that can be downloaded and installed once forever. What I used most is Libreoffice Draw: it imports a PDF, edit it as if it were a file in its own format, export as PDF again. It's not the only choice. Firefox has had a vanilla PDF editor since last year: download a PDF or drag one inside the browser window, edit it, save it. It's enough to add a PNG of my signature and fill out forms.