Annotations, selection or font preferences are only supported for text based formats (epub, mobi, kindle), but not for pdf or comics. In addition, ebooks must conform to official standards.

Content without structured or semantic markup can not always be displayed correctly and creating annotations can fail. For example, if text is contained in div or span elements instead of paragraphs or when local styles are used, a parser can not know its meaning or render it correctly.

This is usually a problem with older formats or “low quality” books. What sometimes helps is to convert such files to a newer format like EPUB 2 with calibre or other programs.

Calibre – E-book conversion:
https://manual.calibre-ebook.com/conversion.html
https://manual.calibre-ebook.com/faq.html#e-book-format-conversion

Page number and total is only available for pdf and comic books. For text based formats (epub, mobi, kindle), it just shows the page/total of the current chapter.

Number of pages for these formats is relative and depends on the screen size, orientation, font or layout. It would be different on your iPhone or iPad and every time you change a reader preference.

Yomu displays the percentage in the library and instead uses a relative content outline at the bottom of the reader. Like in a physical book, this gives you an indication if you are at the beginning, middle or end and also lets you see the remaining chapters.

Additional information is available in the Get Started Guide.

Text selection, highlights or search are not supported for PDF documents. Annotations, custom layout options or theme and font preferences are not planned at the moment.

As an alternative, you could use the Apple Quick Notes integration to create notes linked to the app. Refer to the Quick Notes FAQ for more details. Or you could also try a PDF to EPub converter such as Calibre or one of the various online services mentioned on Reddit and other forums.

Yomu is an ebook reader mainly focused on text based formats (epub, mobi, kindle). PDF support is rather basic, it’s just a viewer. For more advanced features, it’s recommended to use a dedicated app like Adobe Acrobat Reader or PDF Viewer Annotation Expert.

Whenever possible, try to buy or download books as EPub files instead of PDF documents. EPub (short for electronic publication) is a format much better suited for ebooks: it’s reflowable and automatically adapts to the size of your device and is ideal for text highlighting and notes or to adjust custom layout, theme or font preferences.

Due to technical limitations, cross-page text selection is not supported for page layout.

As a workaround, you would need to change to scroll content layout. Tap the top right preferences button (Aa), navigate to Layout > Content to select vertical scrolling. Further details on preferences can be found in the guide.

Yomu uses Apple’s default text selection, which can sometimes be unreliable. What usually works best is to long press on an individual word and adjust the selection handles afterwards as noted in the known issues.

Search is only supported for text based formats (epub, mobi, kindle) and not for pdfs or comics.

But search only works in books with semantic content. If a document contains unstructured markup, it can’t always be indexed correctly. For example, text needs to be in paragraphs as otherwise it’s unclear what the textual content is.

It should work with most books, but for some it fails. This is often a problem with old formats or converted books that lack any structured content.

Loading time depends on the structure and content of a book. Standard compliant ebooks split content into one file per chapter and should render quite fast. But when this is not the case, the complete book may need to be loaded and it can take a while for the entire layout to be calculated or it can even fail. Likewise if there are unoptimised styles, it will take longer to display a book.

What you can do is change the layout preferences from page to scroll, which should load your book faster. Otherwise, you would have to edit such books to split content chapters into individual files and optimise style formats.

For example with Calibre, you can edit books and either use the preview panel to manually split long html files or automatically by e.g. title or certain classes. Converting a book will also remove unnecessary styles and clean it up.

Refer to the manual for more information:
https://manual.calibre-ebook.com/conversion.html
https://manual.calibre-ebook.com/edit.html#splitting-html-files

Apple’s WebKit component is used to render content, which does not support user-installed fonts. This is due to privacy concerns, as it would allow apps to fingerprint and track users based on their installed custom fonts (see Tracking Prevention in WebKit).

Yomu includes several optimized reader fonts and you can choose any preinstalled system font. From the preferences you can also select the “original” book font, but this will only work when it’s either a system font or when the corresponding font files are bundled with the book.

Ebooks are usually split into individual files per chapter and Yomu displays them as such. When you reach the end with vertical scrolling enabled, you will need to load the next one either with the navigation buttons at the bottom or keyboard shortcut to open the next chapter (Shift + Command + Arrow Right).

But you can also “overscroll” with a trackpad, magic mouse or similar device: when at the bottom, pull up a little and release to open the next chapter. Likewise, pull down to go to the previous chapter when you are at the top.